Facilitators and barriers of children’s participation in nutrition, physical activity, and obesity interventions: a systematic review

Abstract

Background:

Recruitment of children into clinical trials is challenging. Most systematic reviews exploring facilitators and barriers of child recruitment in clinical trials are related to drugs or experimental treatments for various health conditions. This may differ in nutrition, physical activity, and obesity interventions.

Objective:

To conduct a systematic review of facilitators and barriers for children’s participation in nutrition, physical activity, and obesity interventions from the perspective of parents, children, and researchers.

Methods:

Studies were identified from 5 databases and restricted to children 2-18 years and the English language. Studies without results on facilitators and barriers of recruitment were excluded.

Results:

423 records were identified; 94 duplicates and 269 unrelated records were initially excluded; 60 records were reviewed for full-text and subsequently 34 were excluded, for a total of 26 included studies. The top barriers for recruiting children into clinical trials were time constraints, understanding of clinical trial information or complexity of consent/trial info, and transportation/lack of childcare. The most common facilitators were benefits to others and self, compensation/incentives, physician recommendations/referrals, and support.

Conclusions:

These barriers and facilitators should be addressed in future studies to assist in the successful recruitment of children into nutrition, physical activity, and obesity interventions.

Introduction

Recruitment of participants into clinical trials is challenging ¹. About 50-70% of clinical trials do not reach the target sample size due to low or slow recruitment.^1-5 This may negatively impact a study, leading to early termination, delay of the trial, loss of funding, higher cost, high stress, low statistical power, and generalizability, among others.^5-8 Further challenges in recruitment can be faced when conducting pediatric clinical trials.^9,10 Children are perceived as a vulnerable population, and often, are ineligible for trial participation due to a lower prevalence of health conditions among this age group. In addition, the process of getting parents’ consent can be complex.⁹

Including children in clinical trials is important for testing different interventions geared towards optimizing their health. There is enough evidence showing that early lifestyle interventions positively impact the risk of non-communicable chronic diseases at an early stage, which could have a large impact on public health.⁸ Despite this, most intervention studies are on adults and the results of these studies have been extrapolated to children, which may not be the best and safest practice.^8,11 However, pediatric clinical trials have been rapidly increasing since 1998, when the National Institutes of Health released its policy for the inclusion of children in clinical research.¹² Because a key factor for succeeding in clinical trials is the timely recruitment of the target sample, it is crucial to understand the barriers and facilitators for enrolling children. This would guide researchers towards an effective and successful recruitment process. Limited information on parents’ and children’s perspectives about their participation in clinical trials has shown engagement of children and their families in clinical research as more complex compared to studies in adults. For example, an important facilitator identified in pediatric clinical trials is the prominent role of the pediatrician’s trial referral and endorsement.^13,14 Ethical considerations for children's inclusion, particularly the process of parents deciding to allow a child’s participation, are central. ¹⁵ Compensation (amount and type) and cost for the children and their families are also relevant factors.⁹

Few systematic reviews have explored aspects related to the recruitment of children into clinical trials; the available reviews have focused on studies recruiting children into drug trials or other trials treating health conditions such as cancer, diabetes, mental health disorders, muscular or skin disorders, or disabilities, among others.^16-19 Facilitators and barriers for recruiting children may differ in less invasive and low-risk studies aiming to improve nutrition, physical activity, and prevent or treat obesity.

To our knowledge, only one systematic review conducted by Robinson et al (2016)¹⁷ evaluated the barriers and facilitators of child recruitment for clinical trials addressing a wide range of medical conditions. Such review¹⁷ included studies related to the treatment of behavioral problems, that had a quantitative design, that was conducted among children 0-12 years old, and that were published up to 2012; only one nutrition study was included. Therefore, it is important to evaluate the different perceptions of the facilitators and barriers for recruiting children into nutrition, physical activity, and obesity interventions by parents and children, and also by researchers. This information could provide insights to address some of the barriers and leverage the facilitators for successfully recruiting children. The present systematic review included quantitative and qualitative studies exploring facilitators and barriers of children's participation in nutrition, physical activity, and obesity interventions from the perspective of the parents and children as well as the perspective of researchers.

Methods

Search strategy

The Prisma Reported Guidelines were used when preparing the systematic review.²⁰ An electronic search was carried out for articles on January 2021 from five databases: PubMed, Agricola, Cumulative Index to Nursing and Allied Health Literature (CINAHL), Embase, PsycInfo. References of identified studies were also reviewed. The search was restricted to peer-reviewed studies published in English focused on quantitative and qualitative studies exploring facilitators and barriers for the recruitment of children (2-18 years) in nutrition, physical activity, and obesity interventions. Included search or key terms were: (motivators OR barriers OR facilitators OR predictors) AND recruitment AND perception AND (parents OR children) AND clinical trial AND (diet OR nutrition OR obesity OR research OR physical activity OR prevention). Recruitment status was defined as either a participant enrolled in the study or approached to be enrolled. A sample query for PubMed is included in Table 1.

Table 1.

PubMed search strategy for the systematic review exploring facilitators and barriers of children participation in nutrition, physical activity, and obesity interventions

Search	Query	Items found
#1	Search: ("facilitate"[All Fields] OR "facilitated"[All Fields] OR "facilitates"[All Fields] OR "facilitating"[All Fields] OR "facilitation"[All Fields] OR "facilitations"[All Fields] OR "facilitative"[All Fields] OR "facilitator"[All Fields] OR "facilitator s"[All Fields] OR "facilitators"[All Fields]) AND ("recruit"[All Fields] OR "recruited"[All Fields] OR "recruiter"[All Fields] OR "recruiters"[All Fields] OR "recruiting"[All Fields] OR "recruitment"[All Fields] OR "recruitments"[All Fields] OR "recruits"[All Fields]) AND ("child"[MeSH Terms] OR "child"[All Fields] OR "children"[All Fields] OR "child s"[All Fields] OR "children s"[All Fields] OR "childrens"[All Fields] OR "childs"[All Fields]) AND ("clinical trial"[Publication Type] OR "clinical trials as topic"[MeSH Terms] OR "clinical trials"[All Fields]) AND ("diet"[MeSH Terms] OR "diet"[All Fields])	25
#2	Search: ("facilitate"[All Fields] OR "facilitated"[All Fields] OR "facilitates"[All Fields] OR "facilitating"[All Fields] OR "facilitation"[All Fields] OR "facilitations"[All Fields] OR "facilitative"[All Fields] OR "facilitator"[All Fields] OR "facilitator s"[All Fields] OR "facilitators"[All Fields]) AND ("recruit"[All Fields] OR "recruited"[All Fields] OR "recruiter"[All Fields] OR "recruiters"[All Fields] OR "recruiting"[All Fields] OR "recruitment"[All Fields] OR "recruitments"[All Fields] OR "recruits"[All Fields]) AND ("child"[MeSH Terms] OR "child"[All Fields] OR "children"[All Fields] OR "child s"[All Fields] OR "children s"[All Fields] OR "childrens"[All Fields] OR "childs"[All Fields]) AND ("clinical trial"[Publication Type] OR "clinical trials as topic"[MeSH Terms] OR "clinical trial"[All Fields]) AND ("nutrition s"[All Fields] OR "nutritional status"[MeSH Terms] OR ("nutritional"[All Fields] AND "status"[All Fields]) OR "nutritional status"[All Fields] OR "nutrition"[All Fields] OR "nutritional sciences"[MeSH Terms] OR ("nutritional"[All Fields] AND "sciences"[All Fields]) OR "nutritional sciences"[All Fields] OR "nutritional"[All Fields] OR "nutritionals"[All Fields] OR "nutritions"[All Fields] OR "nutritive"[All Fields])	25
#3	Search: ("facilitate"[All Fields] OR "facilitated"[All Fields] OR "facilitates"[All Fields] OR "facilitating"[All Fields] OR "facilitation"[All Fields] OR "facilitations"[All Fields] OR "facilitative"[All Fields] OR "facilitator"[All Fields] OR "facilitator s"[All Fields] OR "facilitators"[All Fields]) AND ("recruit"[All Fields] OR "recruited"[All Fields] OR "recruiter"[All Fields] OR "recruiters"[All Fields] OR "recruiting"[All Fields] OR "recruitment"[All Fields] OR "recruitments"[All Fields] OR "recruits"[All Fields]) AND ("child"[MeSH Terms] OR "child"[All Fields] OR "children"[All Fields] OR "child s"[All Fields] OR "children s"[All Fields] OR "childrens"[All Fields] OR "childs"[All Fields]) AND ("clinical trial"[Publication Type] OR "clinical trials as topic"[MeSH Terms] OR "clinical trial"[All Fields]) AND ("obeses"[All Fields] OR "obesity"[MeSH Terms] OR "obesity"[All Fields] OR "obese"[All Fields] OR "obesities"[All Fields] OR "obesity s"[All Fields])	36
#4	Search: ("facilitate"[All Fields] OR "facilitated"[All Fields] OR "facilitates"[All Fields] OR "facilitating"[All Fields] OR "facilitation"[All Fields] OR "facilitations"[All Fields] OR "facilitative"[All Fields] OR "facilitator"[All Fields] OR "facilitator s"[All Fields] OR "facilitators"[All Fields]) AND ("recruit"[All Fields] OR "recruited"[All Fields] OR "recruiter"[All Fields] OR "recruiters"[All Fields] OR "recruiting"[All Fields] OR "recruitment"[All Fields] OR "recruitments"[All Fields] OR "recruits"[All Fields]) AND ("child"[MeSH Terms] OR "child"[All Fields] OR "children"[All Fields] OR "child s"[All Fields] OR "children s"[All Fields] OR "childrens"[All Fields] OR "childs"[All Fields]) AND ("clinical trial"[Publication Type] OR "clinical trials as topic"[MeSH Terms] OR "clinical trial"[All Fields])	291
#5	Search: ("barrier"[All Fields] OR "barrier s"[All Fields] OR "barriers"[All Fields]) AND ("recruit"[All Fields] OR "recruited"[All Fields] OR "recruiter"[All Fields] OR "recruiters"[All Fields] OR "recruiting"[All Fields] OR "recruitment"[All Fields] OR "recruitments"[All Fields] OR "recruits"[All Fields]) AND ("child"[MeSH Terms] OR "child"[All Fields] OR "children"[All Fields] OR "child s"[All Fields] OR "children s"[All Fields] OR "childrens"[All Fields] OR "childs"[All Fields]) AND ("clinical trial"[Publication Type] OR "clinical trials as topic"[MeSH Terms] OR "clinical trial"[All Fields]) AND ("diet"[MeSH Terms] OR "diet"[All Fields])	26
#6	Search: ("barrier"[All Fields] OR "barrier s"[All Fields] OR "barriers"[All Fields]) AND ("recruit"[All Fields] OR "recruited"[All Fields] OR "recruiter"[All Fields] OR "recruiters"[All Fields] OR "recruiting"[All Fields] OR "recruitment"[All Fields] OR "recruitments"[All Fields] OR "recruits"[All Fields]) AND ("child"[MeSH Terms] OR "child"[All Fields] OR "children"[All Fields] OR "child s"[All Fields] OR "children s"[All Fields] OR "childrens"[All Fields] OR "childs"[All Fields]) AND ("clinical trial"[Publication Type] OR "clinical trials as topic"[MeSH Terms] OR "clinical trial"[All Fields]) AND ("nutrition s"[All Fields] OR "nutritional status"[MeSH Terms] OR ("nutritional"[All Fields] AND "status"[All Fields]) OR "nutritional status"[All Fields] OR "nutrition"[All Fields] OR "nutritional sciences"[MeSH Terms] OR ("nutritional"[All Fields] AND "sciences"[All Fields]) OR "nutritional sciences"[All Fields] OR "nutritional"[All Fields] OR "nutritionals"[All Fields] OR "nutritions"[All Fields] OR "nutritive"[All Fields])	45
#7	Search: ("barrier"[All Fields] OR "barrier s"[All Fields] OR "barriers"[All Fields]) AND ("recruit"[All Fields] OR "recruited"[All Fields] OR "recruiter"[All Fields] OR "recruiters"[All Fields] OR "recruiting"[All Fields] OR "recruitment"[All Fields] OR "recruitments"[All Fields] OR "recruits"[All Fields]) AND ("child"[MeSH Terms] OR "child"[All Fields] OR "children"[All Fields] OR "child s"[All Fields] OR "children s"[All Fields] OR "childrens"[All Fields] OR "childs"[All Fields]) AND ("clinical trial"[Publication Type] OR "clinical trials as topic"[MeSH Terms] OR "clinical trial"[All Fields]) AND ("obeses"[All Fields] OR "obesity"[MeSH Terms] OR "obesity"[All Fields] OR "obese"[All Fields] OR "obesities"[All Fields] OR "obesity s"[All Fields])	39
#8	Search: ("barrier"[All Fields] OR "barrier s"[All Fields] OR "barriers"[All Fields]) AND ("recruit"[All Fields] OR "recruited"[All Fields] OR "recruiter"[All Fields] OR "recruiters"[All Fields] OR "recruiting"[All Fields] OR "recruitment"[All Fields] OR "recruitments"[All Fields] OR "recruits"[All Fields]) AND ("child"[MeSH Terms] OR "child"[All Fields] OR "children"[All Fields] OR "child s"[All Fields] OR "children s"[All Fields] OR "childrens"[All Fields] OR "childs"[All Fields]) AND ("clinical trial"[Publication Type] OR "clinical trials as topic"[MeSH Terms] OR "clinical trial"[All Fields])	254

Mesh=medical subject headings.

Inclusion and exclusion criteria

The PICOS framework was used to guide our eligibility criteria (Table 2)²¹.

Table 2.

Study Eligibility Criteria using the PICOS framework²¹

PICO	Included	Excluded
Participants	Children aged 2-18 years	Adult participants (19 years and older)
Intervention	Obesity, dietary, and physical activity	Studies testing interventions and/or drugs to treat conditions such as cancer, diabetes, mental disorders, disabilities, skin disorders, respiratory disorders, and infections
Comparison	Any, including none
Outcomes	Facilitator or barrier for recruiting children into clinical trials	No results on facilitator or barriers of recruitment and other systematic reviews
Study Methods	Any study published up to the search date was considered	Conference presentations, abstracts, protocols, reviews, and dissertations

Study selection and data extraction

Titles and abstracts of identified studies were independently screened for eligibility by two reviewers (CP and YL) against the inclusion and exclusion criteria. Articles initially classified as ‘included’ were further reviewed using the full-text paper. Upon full-text review, any uncertainties were cleared by a second reviewer (MT) through discussions between the reviewers to resolve the divergence. Full-text screening and data extraction were conducted by at least 2 reviewers and all were reviewed for accuracy by CP. A data extraction sheet was developed specifically for this systematic review. This included: author, year of publication, study name and aims, sample characteristics, setting, dates of study, ethical considerations, outcomes, methods, reporting group, facilitators, barriers, and other relevant results. All reasons for exclusion are documented in the PRISMA diagram (Figure 1).

Figure 1.

Flow diagram of the records identified in the systematic review assessing facilitators and barriers of children participation in nutrition, physical activity, and obesity interventions as reported by children, parents, and researchers.

Appraisal of the quality of each study

The critical appraisal of the methodological quality of qualitative, quantitative, and mixed methods studies was conducted using the Mixed Methods Appraisal Tool (MMAT),²² a tool specifically designed for systematic reviews. MMAT includes two screening questions applicable to all study designs and five key questions about the quality of each type of study design. Trials that satisfied most criteria were considered of higher quality.

Appraisal of the certainty of the evidence

The Grading of Recommendations Assessment, Development, and Evaluation (GRADE) was used as the framework for summarizing the evidence and making an overall assessment of confidence of the themes identified in quantitative studies.²³ Key findings were assessed and graded for confidence (‘high’, ‘moderate’, ‘low’, or ‘very low’ quality) based on study limitations, inconsistency of results, indirectness of evidence, imprecision, and reporting bias. For qualitative studies, the GRADE-CERQual (Confidence in Evidence from Reviews of Qualitative research) tool was used.²⁴ Key findings were assessed and graded for confidence (‘high’, ‘moderate’, ‘low’, or ‘very low’) based on methodological limitations, coherence, adequacy, and relevance. GRADE was implemented among themes with more than one quantitative study. Similarly, GRADE-CERQual was used only among themes with more than one qualitative study. The coding for both GRADE and GRADE-CERQual was done by two coders (PC and JC). Disagreements were discussed with CP.

Coding of facilitators and barriers

Facilitators and barriers were categorized by the role of the person responding or the data source: (1) parents and children; or (2) research staff. Facilitators were defined as factors that would lead to recruitment into clinical trials. Barriers were defined as factors that deterred recruitment into clinical trials. Common themes were identified from the included studies by the two coders (PC and JC). The themes were explained based on the included study’s findings and verbatim quotes.

Results

Study selection

From 423 records found in the search, 414 records were identified from the five databases searched and 9 from other additional sources. After removing duplicates, a total of 329 records were screened for eligibility by title and abstract review, in which 269 records were excluded (Figure 1). The remaining 60 records were full text reviewed, after which an additional 34 records were excluded (Figure 1). Thus, 26 records were included in the present review. Tables 3 and 4 show the data extraction sheets.

Table 3.

Data extraction for studies included in the systematic review assessing facilitators and barriers of children participation in nutrition, physical activity, and obesity interventions from the parents’ and children’s perspectives

Author (s)	Study name or aim	Type of study	Population	Setting & dates of study	Ethics	Outcome (s)	Methods	Facilitators	Barriers
Cruz et al. (2014)44	Child Health Initiative for Lifelong Eating and Exercise (CHILE)	Mixed methods (RCT)	1,879 children, 655 parents, 7 grocery stores, and 14 healthcare providers from low-income communities in rural areas with a high prevalence of American Indian	16 Head Start centers in New Mexico, USA. 2006-2010	IRB approval and consent obtained from participants	Obesity prevention program	Interviews were conducted with parents being recruited for a multi-level, group RCT, and review of study records. Interviews in English or Spanish based on preference. Study enrollment was done all year for 17 months.	feedback to intervention sites; revised permission forms; phone reminders; increased site visits; over-scheduling of interviews; use of community champions; bilingual/bicultural facilitators; convenient location; centers <150 miles to minimize travel; face-to-face recruitment; not targeting specific age groups; > recruitment & smaller sites; setting goals for the number of interviews per site; monetary incentives; inclusion of physician in the recruitment team; physicians recruiting physicians to serve as role moles, support study goals, & participate in family events meals provided at recruitment	No shows at the mandatory orientation parents forgot to return permission slips lack of adequate information to make an informed decision; negative comments from others about participating in trials no shows for the interview; work schedules and obligations; parent interviews lasted approximately 1-2 hours
Drews et al. (2009)45	Recruitment and retention strategies and methods in the HEALTHY study	Mixed methods (RCT)	59 parents of 8th graders	University clinic setting (California, Texas, and North Carolina), USA. 2006-2009	IRB approval and consent & assent obtained from participants	Prevention of modifiable risk factors for type 2 diabetes in youth	Semi-structured phone interviews on reasoning for participating (n=40)or not participating (n=19)in the visit (anthropometrics and blood draw)	Parent’s perspective: family history of diabetes; learn about child's health status; convenience of having the screening at school; no travel time needed for data collection event uncertainty on susceptibility for diabetes in childhood or adulthood; Children’s perspective: monetary incentives The recruitment period extended through the end of the health screening (data collection event)in each school.	Parent’s perspective from participating children: concern of the blood draw (for oral glucose tolerance test); potential health; sending child to school fasting; Parent’s perspective from non-participating children: lack of understanding of informed consent; child's refusal; lack of time; child forget to give parents the forms; confusion about the consent copy to sign & one to keep; language & communication barriers (although all materials were in English & Spanish)
Edwards et al. (2016)41	Implementation issues associated with the delivery of Bristol Girls Dance Project (BGDP)	Mixed Methods (RCT)	571 girls aged 11-12 years old. Qualitative data collected from 59 girls, 10 dance instructors, and 9 schools involved in BGDP	18 secondary schools (9 intervention, 9 control)in the Greater Bristol area, UK	IRB approval and consent obtained from participants	Physical activity intervention	20-week school-based intervention (40 sessions, 2 sessions per week for 20 weeks); each session was 75 minutes; 9 focus sessions conducted at the school of 42 min; Dance instructor interviews: were 67 min School contact interviews 30 min)	Friend involvement and recruiting friendship groups; Familiar recruiter to participants; Endorsements from other places; Detail information about tasks and requirements from participants; Monetary incentives; Promoting the importance and esteem of the university-led research; Children could try a new activity; Convenient location;	Recruiter not familiar with the participants Recruiting children in the first few weeks of school year
Fleming, J et al. (2015)46	Evaluation of recruitment methods for a trial targeting childhood obesity.	Mixed Methods (RCT)	115 families with obese children aged 6–11 years	Medical centers, schools, community. W Midlands, UK. 2010-2014	IRB approval and consent & assent obtained from participants	Obesity treatment	Evaluation of study records, questionnaires, recruited parents. Recruitment: 24 months (2012-2013); Data collection for 10 weeks; sessions 2.5 hours/wk on Saturdays; Duration of focus interview: 20 minutes	recognized child as overweight; looking for support or had previously accessed services; receiving study letter from physician; 4 of4% participants were recruited by this referral receiving study letter from physician a second time.
Ghai NR et al. (2014)52 (Drews et al. 2009)45	Recruitment among families for the Obesity Prevention Tailored for Health Study	Mixed Methods (RCT)	361 parents & children 10-12 years enrolled in a large managed-care organization	Claremont Graduate University, Kaiser Permanente Southern California, USA. 2010-2011	IRB approval and consent & assent obtained from participants	Obesity prevention	Recruitment staff called potential participants and recorded reasoning and reviewed medical records. Recruitment: Jun 2010 – Nov 2011 Intervention: 18 weeks Baseline visit: 2 hours	participation was higher if child was overweight or obese; participation higher among those with more outpatient visits and more flu vaccinations.	Acceptors not randomized: inability or unwillingness to come to baseline visit; lack of time or no longer interested; no reason/other/missing Refusal to participate: lack of interest and time; do not need the intervention no reason/other/missing
Gillespie J et al. (2015)29	A social marketing approach to understanding triggers and barriers on weight management	Qualitative	27 parents/caregivers of primary and secondary school children	Different settings in local communities, UK. 2010	IRB approval and consent obtained from participants	Weight management	Four focus group discussions (~2 hours each in 4 sites)with semi-structured topic guide and blob tree visuals. Recruitment: March 2010	emotional/social skills that would benefit their child (confidence and self-esteem); support from other parents; gain back control; acceptance help from others; easy to implement; aspiration/goals: happy child; information on how, where, and when to access a service; Non-stigmatizing, a valuable sense of community;	lack of control: 'the problem is too big'; desire to avoid conflict: "It's easier just to give in’; no good reason: 'the case isn't proven'; fear of confronting issues: 'I can't bear to raise it, and I don't want to make things worse'’ uncertain where to turn: 'I don't know what specialist support is out there'
Grow HM et al. (2013)30	Understanding family motivations and barriers to participation in community-based programs for overweight youth	Qualitative	23 parents of children 8-14 years old (required to be referred by health care provider)	YMCA sites, USA. 2008-2009	IRB approval and consent obtained from participants	Obesity prevention	In-person interviews about intention-motivation, environmental constraints, support, and skills to participate, with open-ended questions Data collection: Fall 2008 – Winter 2009; Intervention: 18 weeks, with 90 min sessions twice weekly for 12 weeks, then weekly for 6 weeks	exposure to knowledge and behaviors; concern for weight and/or other health factors; support/assistance from staff and similar families in the intervention; help with parenting for health behaviors and reinforcement; spending time with child; parent's persistence despite child being reluctant.	scheduling conflicts; too much time and too long; no Saturday sessions; not perceiving as needed; long distance from home; concern the program would not be 'ongoing'; lack of support from family; bad traffic; darkness and rain Program only offered in English; no interpreters
Hamilton J et al. 2014)47	Changing eating behaviors to treat childhood obesity in the community: ComMando	Mixed Methods (RCT)	37 children 5-11 years old (required to be referred by health care provider)	Clinical and home setting, UK. 2012-2013	IRB approval and consent obtained from participants	Obesity treatment	Phone interview to identify barriers to participation. Pilot phase was 9 months before trial (April 2012 – December 2012). Intervention was for 12 months, with 9 visits & 3 support phone calls. Focus group: 3 visits	From 5 decliners: encouragement from children; concerns about child's weight and diet; shared activity for parents & children to manage weight; great opportunity due to lack of weight programs; From acceptors: enough information to make an informed decision; long-term health benefits; helping other families; children want to stop bullying and want to be healthier.	From decliners: time conflicts; misunderstanding of the trial worried about having to do group work; long duration; lack of commitment; Only offered in English
Jago et al. (2013)42	Process evaluation of the Teamplay parenting intervention pilot: implications for recruitment, retention, and course refinement	Mixed Methods (RCT)	16 Parents of 6-8y old children in the intervention group and 10 from the control group for call interviews	Bristol, UK	IRB approval & consent obtained from participants	Physical activity and screen viewing intervention	Interviews were conducted via phone. 6 parents in the intervention group received face-to-face interviews due to language barriers. Data collection: Mar-Jun 2011. Main study had 8 visits of 2h (once weekly for 8 weeks). 7 focus groups done in 2012 (within a month of the end of trial of 12-58 mins for intervention & 8-13 mins for control group).	Improve their parenting skills; Increasing knowledge about how to change activity behavior; Intervention resonated with parents; An active parenting course; Effective communication to parents; Promotional materials; Free childcare; Encouraged by a friend; Helping with a research project; Peer learning; Randomization was clear; Course leaders were friendly; Convenient location; Text reminders; Accommodated participants whom English was not the 1st language	Did not appeal to them until face-to-face interaction; Misunderstood course to be specifically for parents with problems; Initially wasn’t clear that the courses were for a research project; Attending a course with new people; Work and other commitments.
Jago et al. (2012)31	Designing a Physical Activity Parenting Course: Parental Views on Recruitment, Content and Delivery.	Qualitative	Parents of children 6-8y (29 females, 3 males)for call interviews (n=32)and for the online survey (n=750)	Schools, children’s centers or nurseries, healthcare surgeries and local projects in Bristol, UK. 2011	IRB approval and consent obtained from participants	Obesity prevention	Interviews with parents and an anonymous online survey that was distributed via a national parenting website. Data collection: Jan-Feb 2011. Online survey data collection: Sep-Oct 2011; Phone interview was 20 mins.	free childcare; different time options for sessions; multiple locations close to participants; recruitment materials aligned with the desired content; varied and wide-reaching recruitment methods	being busy or having other commitments; financial cost of transportation; need for childcare.
Nicholl et al. (2018)32	Parental opinions on improving clinical dietary trials for young children.	Qualitative	17 parents of children 2-6 years were invited to participate in one of the three focus groups	Playgroups in Perth, Australia	IRB approval and consent obtained from participants	Dietary trials	In person or online focus sessions (3 sessions each of 50 minutes). Parents had the option of attending 2 face-to-face, 1 online.	Altruism	needle fear; parents were hesitant about blood and stool samples unless they included additional analyses relevant to them; understanding and ability to cope; lack of awareness of current dietary guidelines; randomization; time commitment (near recruitment site, ~30 km) or online; intervention for their child; confronting tests positive; Non-English-speaking participants were excluded
Rice et al. (2008)48	Successes and barriers for a youth weight-management program.	Mixed Methods (RCT)	Parents of children 7-17 years being recruited in the program on exercise.	Private health club in Brentwood, TN, USA	Private study: parents paid to enroll children in study	Weight management	Review of recruitment methods from study records and follow-up with interviews to participating pediatricians and referred families. Intervention: 12 months with 8 nutrition counseling sessions (3 sessions/wk first 3 months; 1 session/wk next 3 months, and then 1 session/mo), each 60 minutes	Familiarity with the facility; desire to change; child's overweight status early; inability to make the changes needed for the child themselves; clear understanding linking weight to health; physician referral; word-of-mouth and direct consumer marketing	school recruitment was very low cost; preferred to help their child on their own; facility too far from their home.
Speirs et al. (2016)33	Recruitment and retention into the Text2bHealthy, a text message-based health education program	Qualitative	1355 parents enrolled in Text2BHealthy (different races/ethnicities)	Food Supplement Nutrition Education program & schools. Maryland, USA. 2012-2013	IRB approval and consent obtained from participants	Nutrition and physical activity	3 post-test surveys and 4 focus groups to measure program awareness, satisfaction, enrollment barriers, among others. Recruitment: Feb-May 2012. Data collection: May-Jun 2012. Sent 3 reminders/wk		inability to enroll; cost to participate; enrollment of non-parents: people who were not parents at participating elementary schools had enrolled; hard to reach with recruitment materials;
Spittaels et al. (2007)49	Review of participation in an online tailored physical activity program the internet	Mixed methods (RCT)	1740 children aged 10-18 years and parents aged 20-55 years.	Primary and secondary schools, Belgium	IRB approval and consent obtained from participants	Physical activity	Review of reply cards of parents during the recruitment process Parental intervention: 1 online survey (controls) and 2 online surveys (intervention); Children: 1 survey at school	mothers more interested to participate than fathers; parents of medium or high SES more interested than parents of low SES; being employed predicted having interest in participating--but when persons were interested, this variable could no longer predict further participation.	child already involved in a lot of physical activity; no interest; not having a desktop computer or Internet access.
Buscail et al. (2018)43	Recruitment of precarious families in an interventional study: Lessons from the French: “Fruits and vegetables at home” FLAM Trial“	Mixed Methods	95 families with at least one child from 3 to 10 years old.	Community centers or at home, France, 2015-2017.	IRB approval and consent obtained from participants.	Nutrition	Face-to-face questionnaires. Children older than 5 years were directly interviewed. March to September 2017, qualitative surveys were conducted to assess recruitment.		Comprehension/communication issues with the recruiters; Lack of time; Mistrust from some people when they were solicited;

RCT: randomized clinical trials; SES: socio-economic status; UK: United Kingdom; USA: United States of America

Table 4.

Data extraction for studies included in the systematic review assessing facilitators and barriers of children participation in nutrition, physical activity, and obesity interventions from the researchers’ perspective

Author (s)	Study name or aim	Type of study	Population	Setting and dates of study	Ethics	Outcome (s)	Methods	Facilitators	Barriers
Blanchet et al. (2015)36	Strategies and challenges in recruiting black immigrant mothers for a community-based study.	Mixed methods (non RCT)	259 mothers of 6-12-year black immigrant children of African and Caribbean decent.	Ottawa, Ontario, Canada. 2014 - 2015	IRB approval and consent & assent obtained from participants	Diet	Review of calling lists, consultation with recruiters, verification of emails, and participants’ calls. Interviews were conducted at participants’ home in French or English	short time; immediate and meaningful distribution of incentives; convenient time and place (church, home, workplace).	inability to provide translation; mistrust of white researchers advancing own career; immigrants & refugees concerned about how their personal information would be used and shared; afraid of being judged; no interest.
Chang et al. (2009)50	Participant recruitment and retention in a program to prevent weight gain in overweight mothers.	Mixed Methods (RCT)	129 low-income overweight young mothers with children 0-3.5 years	Southern Michigan Woman Infant Children (WIC) programs, USA. 2007	IRB approval and consent & assent obtained from participants	Diet, physical activity, stress management	Identification of predictors from data review and recruiters' log notes.	emphasizing confidentiality; video of procedures, protocols, and incentives; culturally sensitive recruiters; collaboration with WIC-university; monetary incentives; respect & rapport from staff; speaking to one mother	lack of interest because of their previous failures with weight loss programs.
Croyden et al. (2018)51	Lessons learnt from the child obesity management program in Australia: PEACH™.	Mixed Methods (RCT)	353 parents of children 5-17 years	PEACH study. Queensland, Australia. 2011-2016	IRB approval and consent & assent obtained from participants.	Obesity	Narrative review of recruitment strategies and evaluation of study records.	Self-referral (via website and/or toll-free number) most effective; Referral from health professional or hospital waiting list; advertisements in school newsletters, media and print advertising	N/A
Cruz et al. (2014)44	Child Health Initiative for Lifelong Eating and Exercise (CHILE).	Mixed methods (RCT)	1,879 children, 655 parents, 7 grocery stores and 14 healthcare providers from low-income communities in rural areas with high prevalence of American Indian	16 Head Start centers in New Mexico, USA. 2006- 2010	IRB approval and consent & assent obtained from participants. Tribe also reviewed protocols, agreements, and resolutions and provided a letter of support.	Obesity prevention program	Interviews conducted with parents being recruited for a multi-level, group RCT and review of study records.	Use of reminder calls the day before and the morning of the interviews Spending more days at smaller sites to recruit from a smaller pool of potential participants Over-recruiting in anticipation of participants failing to come to an appointment Use of a physician member of the research team to contact healthcare providers directly increased participation. Scheduling recruitment meetings over lunch and providing lunch was an efficient use of time and proved to increase participation rates.	Individuals who agreed to an appointment but did not show up for the interview Work schedules and obligations Timing of CHILE family events Funding constraints.
Cui Z et al. (2019)38	Recruitment strategies for the Childhood Obesity Prevention and Treatment Research (COPTR) Consortium.	Mixed Methods (RCT)	1745 parents and children (racially/ethnically diverse; many were recent immigrant families)	family, school, clinic, churches, grocery stores, recreational centers in Cleveland, Minnesota, California, Tennessee, USA	IRB approval and consent obtained from participants. Inclusion of certificate of confidentiality or explicit discussion of the privacy of participant	Obesity	Data review of strategies used. A group of parents preview the consent materials,	flexible study schedules (outside regular work hours); clear detailed recruitment protocols (reading levels of the consent materials were <7th grade); repeated contacts; existing trustful relationships with the community; use of community liaison; tracking database (i.e. Redcap); culturally sensitive staff; face-to-face recruitment; personal style of staff.	long wear of accelerometer; lack of interest; lack of understanding or knowledge of the research; busy family schedules; lack of transportation; narrow eligibility criteria; no value for obesity prevention; long trial commitment; low number of participants; inaccurate phone numbers; inability to reach caregivers.
Czymoniewicz et al. (2017)37	Patterns of participation in the Grow Face-to-Face and Grow Online parenting program.	Mixed Methods (non-RCT)	111 parents with health children 5-10 years old	Local YMCA in central Pennsylvania, USA. 2015-2017	Consent obtained from participants	Obesity prevention	Review of attendance records, surveys and semi-structured, in-depth interviews.	E-gift card incentives	time burden (no additional information was given). too much to do; lack of interpersonal interaction; relevance of program content.
DeFrank et al. (2019)39	Recruitment and retention strategies and lessons learned from the Intervention INC trial.	Mixed Methods (RCT)	Black/AA and Latino children (ages 9–12 years) and their parent/guardian	Community/school-based organizations in low-income neighborhoods. Harlem, New York, USA	IRB approval and consent & assent obtained from participants	Obesity prevention	Review of recruitment strategies.	community & school events; flyers in the community; referrals from friends & other participants; frequent reminders before appointments; relaxed inclusion criteria; partnered with community organizations, schools, etc.; provided education and food; extended recruitment period; increased time in community; Bilingual staff	outdated contact information from community partners; short recruitment target time; frequent no-shows and cancelations for baseline visits; parents provided inaccurate estimates of child’s height and weight; difficulty recruiting children in overweight/obese BMI percentile categories
Fleming et al. (2015)46	Evaluation of recruitment methods for a trial targeting childhood obesity: Families for Health RCT.	Mixed Methods (RCT)	115 families with obese children aged 6–11 years	Medical centers, schools, community, public events. West Midlands, UK. 2010-2014	IRB approval and consent & assent obtained from participants	Obesity treatment	Evaluation of study records and questionnaire and interviews with recruited parents/caregivers. Recruitment: 24 months (2012-2013); Data collection for 10 weeks; sessions 2.5 hours/wk on Saturdays; Duration of focus interview: 20 minutes	targeted letter from healthcare professionals; referrals from healthcare professionals; Posters and flyers posted in schools, clinics, internet, etc.; in-person interviews and q; giving time to families to consider their participation;	unable to contact interested potential participants; intervention activities scheduled only on Saturdays; transportation issues study too long (10 weeks; sessions 2.5 hours/wk).
Gerards et al. (2012)34	Barriers for health care professionals for referring parents of overweight children to an obesity prevention intervention.	Qualitative	16 nurses, physicians and management staff from 11 clinics attending parents of overweight children aged	11 health clinics, Maastrich, The Netherlands. 2010	Consent obtained from participants	Obesity prevention	Semi-structured interviews to health care professionals.	appropriate center to reach youth consistent messages from the different organizations; involvement of different organizations (general practitioners, schools, day-care centers, etc.)	parents do not recognize their child as overweight; lack of enough resources; lack of time for physician to explain the study; lack of involvement from nurses should be more closely lack of study information to health staff; lack of involvement from all relevant stakeholders
Guzman et al. (2009)40	Recruitment and retention of Latino children in a lifestyle intervention.	Mixed Methods (RCT)	159 Latino parents and children	Clinical setting in North Carolina, USA. 2005-2006	IRB approval and consent & assent obtained from participants. Consents were provided in English or Spanish.	Lifestyle intervention	Review of recruitment strategies.	referrals from community pediatric offices; media efforts and community organization outreach; family referrals; wellness van	lack of time (to help with this, clinic time was changed to early evening and Saturdays); family competing priorities; transportation; caring for other children; lack of bilingual staff
Kafka et al. (2008)35	To explore children's motivations and barriers to nutrition research participation.	Qualitative	35 children aged 7–10 years recreational and competitive soccer players	Indoor sports center. Acton, Massachusetts, USA. 2008	IRB approval and consent & assent obtained from participants	Nutrition	Focus group with children to learn how to make research better for children. Main study objectives: examine how the nutrient density and antioxidant content of 3 snacks affected exercise intensity, fatigue, blood glucose (finger prick before and after the match), and other biochemical marker (saliva).	financial incentives; reduce trepidation by "showing them finger pricks; Eating the study snack; being tested	anxiety over finger pricks before and after the match for blood glucose
McCullough et al. (2016)25	Barriers to Recruitment in Pediatric Obesity Trials: Comparing Opt-in and Opt-out Recruitment Approaches.	Quantitative RCT	Investigators of 3 trials in children 2-7 years (CHIRP & LAUNCH) and children 8-12 years (E-FLIP)	10 rural communities in North Central Florida, USA. 2009-2015	Consent obtained from participants	Obesity treatment	Review of opt-in strategies (parents contact researchers in response to mailings) and opt-out strategies (parents send decline postcard in response to mailings).	in the opt-out strategy, families were more likely to have contact with the study staff, be phone screened, and be randomized.	In the opt-in strategies, families were less likely to contact the study and be phone screened, agree to in-person screening, consent to be in the study, meet inclusion and enroll, and be enrolled.
Metayer et al. (2018)26	Recruitment of new immigrants into an RCT: The Live Well Experience.	Quantitative RCT	New immigrant mothers and children from Brazil, Spanish-speaking Latino or Haitian descent with over 10 years in the US and with a child 3-12 years	Community Centers in Somerville, MA, USA. 2009-2011	Consent obtained from participants	Lifestyle intervention	Review of recruitment data to inform ongoing process evaluation.	adjustments in eligibility criteria; broadening outreach to nearby communities; shorter intervention; more community staff (trusted and familiar) for recruitment; highlight of staff experience; flexible schedule; childcare provided; culturally appropriate food; community partnerships & immigrant organizations use of posters and flyers; monetary incentives; reminders of recruitment visit; recruitment subcommittee	stress surrounding childcare arrangements
Nicholson et al. (2006)27	Recruitment and retention strategies in longitudinal clinical studies with low-income populations.	Quantitative RCT	306 mothers 15-42 years of age (AA, non-Hispanic Whites and Hispanics)	Low Income, ethnic neighborhoods in Columbus, Ohio, USA. 2005-2006	Consent obtained from participants	Nutrition	Description of specific strategies employed to successfully recruit and retain participants.	study viewed as part of standard clinical care and not as an experiment; nurse leaders oversaw leaders and interviewers, integrating research into clinical process and helped to form relationship between research staff, clinical staff, and participants.	some mothers felt rushed to get to their appointment; some mothers were busy attending to children; one clinic underwent slow recruitment due to infrastructure change.
Raynor et al. (2009)28	Evaluation of active and passive recruitment methods used in randomized controlled trials targeting pediatric obesity.\	Quantitative RCT	164 families with overweight children 4-9 years	Community health centers, children’s health centers, schools, Internet, radio, newspapers and TV in Massachusetts, USA. 2005-2007	Consent & assent obtained from participants	Weight management	Review of enrollment numbers and cost-effectiveness of active (physician referrals, targeted mailings) vs passive (adds and flyers, word of mouth) recruitment methods.	active strategies (largest number of enrolled and randomized families); passive recruitment methods (less families recruited but better retention from enrollment to randomization)	parents do not identify overweight in their children; inability to complete phone-screening due to phone disconnection; no time to complete the screening; no adults at home by the time of the call; researchers did not identify if parents were contacted by one or several recruitment methods; phone calls were not included in the costs; used TV advertisements for a short period due to cost.

RCT: randomized clinical trials; UK: United Kingdom; USA: United States of America; CHIRP: Community Health Lifestyle Intervention for Rural Preschoolers; LAUNCH: Learning about Activity and Understanding Nutrition for Child Health; E-FLIP: The Extension Family Lifestyle intervention project for Kids

Characteristics of included studies for systematic review

The 26 records included in this review varied in research objectives and study designs. Four studies were randomized clinical trials involving only quantitative evaluation of recruitment (with the review of study records to evaluate recruitment and/or surveys or questionnaires about recruitment).^25-28 Seven were qualitative studies (which included interviews or focus groups with potential participants to inform a future clinical trial).^29-35 Lastly, 16 studies applied mixed methods (which included the review of study records to evaluate recruitment and/or supplementary interviews, focus groups, surveys, or questionnaires about recruitment).^36-51. Fifteen studies questioned parents and children about the facilitators and/or barriers to engaging in clinical trials,^{29,30,46-49,52,31-33,41-45} and within these, only three studies assessed perceptions of both parents and children. ^47,48,52 Also, 15 studies questioned research staff,^{25,26,40,44,46,50,51,27,28,34-39}. From all of these studies, two questioned children and parents and also researchers.^44,46 Fifteen studies evaluated recruitment of children in obesity-related trials,^{25,28,46-48,51,52,29-31,34,37-39,44} and 10 studies in nutrition or physical activity interventions.^{26,27,32,33,35,36,40,45,49,50} Sample size varied from 37-1,879 in the mixed methods studies, 23-306 in quantitative studies, and 16-1,355 in qualitative studies. Lastly, 16 studies were conducted in the United States,^{25,26,40,44,45,48,50,52,27,28,30,33,35,37-39} nine in Europe,^{29,31,34,41-43,46,47,49} two in Australia,^32,51 and one in Canada.³⁶

Study quality and risk of bias

Table 5 shows the study quality using the MMAT. Most studies (n=21) satisfied all quality criteria, suggesting an overall strong study quality. Four studies missed one or two criteria and only three studies had one negative response. Quality issues identified by these five studies were samples that may not be representative of the target population or inadequate randomization and incomplete outcome reports or inappropriate measurements. Although not part of the MMAT, the ethical aspects of each included study were also assessed. All trials reported were approved by internal review/ethical boards and described the consent/assent process.

Table 5.

Quality assessment of included studies in the systematic review exploring facilitators and barriers of children participation in nutrition, physical activity, and obesity interventions, using the MMAT²²

Authors	S1	S2	Question 1	Question 2	Question 3	Question 4	Question 5	Comments on quality appraisal
Qualitative
Gerards et al. (2012)34	Y	Y	Y	Y	Y	Y	Y
Gillespie J et al. (2015)29	Y	Y	Y	Y	Y	Y	Y
Grow HM et al. (2013)30	Y	Y	Y	Y	Y	Y	Y
Jago et al. (2012)31	Y	Y	Y	Y	Y	Y	Y	Not clear how was the transcriptions used or how it was conducted.
Kafka et al. (2011)35	Y	Y	Y	Y	Y	Y	Y
Nicholl et al. (2018)32	Y	Y	Y	Y	Y	Y	Y
Speirs et al. (2016)33	Y	Y	Y	Y	Y	Y	Y
Quantitative RCT
McCullough et al. (2016)25	Y	Y	Y	Y	Y	NR	Y	3 separated studies reported, some lack information to appraise quality
Metayer et al. (2018)26	Y	Y	Y	N	Y	NA	NA	Only baseline data
Nicholson et al. (2011)27	Y	Y	N	Y	Y	NR	Y
Raynor et al. (2009)28	Y	Y	Y	Y	Y	NR	Y
Quantitative descriptive
Spittaels et al. (2007)49	Y	Y	Y	Y	Y	Y	Y
Mixed methods – RCT
Buscail et al. (2018)55	Y	Y	Y	Y	Y	Y	Y
Chang et al. (2009)50	Y	Y	Y	Y	Y	Y	Y
Croyden et al. (2018)51	Y	Y	Y	Y	NR	Y	Y
Cruz et al. (2014)44	Y	Y	Y	Y	Y	Y	NR
Cui Z et al. (2019)38	Y	Y	Y	Y	Y	Y	Y
DeFrank et al. (2019)39	Y	Y	Y	Y	Y	Y	Y
Drews et al. (2009)45	Y	Y	Y	Y	Y	Y	Y
Edwards 2016)41	Y	Y	Y	Y	Y	Y	Y
Fleming et al. (2015)46	Y	Y	Y	Y	Y	Y	Y
Ghai NR et al. (2014)52	Y	Y	Y	Y	Y	Y	Y
Guzman et al. (2009)40	Y	Y	Y	Y	Y	Y	Y
Hamilton J et al. 2014)47	Y	Y	Y	Y	Y	Y	Y
Jago R 2013)42	Y	Y	Y	Y	Y	Y	Y
Rice et al. (2008)48	Y	Y	Y	N	Y	Y	NR
Mixed methods - non-RCT
Blanchet et al. (2017)36	Y	Y	Y	Y	Y	Y	Y	Did not reach the targeted stratifications
Czymoniewicz et al. (2017)37	Y	Y	Y	Y	Y	Y	Y

Y=yes; N=no; NR=not reported; NA: not applicable

Barriers to recruitment

The most common barriers in recruiting children into clinical trials are described below (Table 6):

Table 6.

Meta-summary of barriers for children participation in nutrition, physical activity, and obesity interventions

Theme	Number of studies	GRADE and GRADE- CERQuala	References
Parents’ and children’s perspective
Time constraints	8	GRADE: High GRADE-CERQual: High	30-32,42,43,45,48,52
Understanding of clinical trial information / complexity of consent/trial info	5	GRADE: High GRADE-CERQual: Moderate	32,42,43,45,47
Cost	3	GRADE: N/A GRADE-CERQual: N/A	31,33,48
Relationship between research staff, medical provider, and participant/family	3	GRADE: N/A GRADE-CERQual: N/A	33,41,43
Nature of the intervention	2	GRADE: N/A GRADE-CERQual: N/A	32,47
Study examinations too invasive	2	GRADE: N/A GRADE-CERQual: N/A	32,45
Transportation	2	GRADE: N/A GRADE-CERQual: N/A	30,31
Lack of support from family or friends	2	GRADE: N/A GRADE-CERQual: N/A	30,48
Felt like a “Guinea Pig”	1	GRADE: N/A GRADE-CERQual: N/A	44
Language barrier	1	GRADE: N/A GRADE-CERQual: N/A	45
Research staff’s perspective
Time constraints	4	GRADE: High GRADE-CERQual: High	37,38,40,46
Transportation/lack of child-care	3	GRADE: High GRADE-CERQual: High	38,40,46
Lack of interest	3	GRADE: High GRADE-CERQual: N/A	36,38,50
Study examinations too invasive	1	GRADE: High GRADE-CERQual: High	35
Language barrier	1	GRADE: N/A GRADE-CERQual: N/A	36
Relationship between research staff, medical provider, and participant/family	1	GRADE: N/A GRADE-CERQual: N/A	36
Understanding of clinical trial information/Complexity of consent/trial info	1	GRADE: N/A GRADE-CERQual: N/A	38

^aGRADE and GRADE-CERQual was done among themes with more than one study. N/A: not available because there were not enough studies of each type to evaluate certainty of the theme.

Time Constraints.

This was the most common barrier reported. Parents reported having other commitments such as work and extracurricular activities, among others.⁴² Parents agreed on having both, less leisure time and time for sports for the child, along with the time it took to get to the clinic, and the trial requiring a lot of involvement and childcare responsibilities.^30,31,37,52 Parents also reported being too busy to take part in a research study⁴⁰ or to complete the enrollment paperwork.⁴⁵ Some studies discussed parental preferences towards study sessions,^31,40 some preferred day sessions while those who worked preferred evening sessions.³¹ Other parents only reported time commitments or were unavailable/unwilling to attend the baseline visit.^32,38,48,52 Research staff reported that families declined to participate because they had important issues going on or did not feel it was the right time.⁴⁶ The certainty in the evidence of this theme was considered by GRADE and GRADE- CERQual as high.

Understanding of clinical trial information / Complexity of consent/trial information.

This barrier was mainly reported by parents and children. Difficulty in understanding the forms and the trial resulted in parents declining to participate.^45,47 In some instances, parents did not specify which aspect of the trial information was difficult to understand or the study authors did not clarify further.^32,38 However, all studies were approved by an internal review/ethical boards, with a clear description of the consent/assent process. The certainty in the evidence of this theme was considered by GRADE as high and by GRADE- CERQual as moderate.

Transportation/childcare.

Difficulties in commuting to the clinic or research facility were reported by both groups. Some reported that the location of the clinic and/or research facility was too far from their home⁴⁶ while others reported the families simply lacked access to transportation^30,38 or that the cost of transportation made it difficult to commit to their children’s ability to participate.³¹ Researchers mentioned that lack of childcare was an important barrier.^26,27,40 A study noted that transportation difficulties were mainly seen among those with low socioeconomic status.⁴⁰ The certainty in the evidence of this theme was considered by GRADE and GRADE- CERQual as high.

Facilitators to recruitment

The most common facilitators in recruiting children into clinical trials are described below (Table 7):

Table 7.

Meta-summary of facilitators for children participation in nutrition, physical activity, and obesity interventions

Theme	Numbers of studies	GRADE and GRADE- CERQuala	References
Parents’ and children’s perspectives
Benefit to others and themselves (altruism)	5	GRADE: High GRADE-CERQual: Moderate	29,42,45,47,48
Compensation/incentives	4	GRADE: High GRADE-CERQual Moderate	31,35,41,42,45
Nature of the Intervention	3	GRADE: High GRADE-CERQual: Moderate	29,30,42
Support from family and friends	3	GRADE: High GRADE-CERQual: Moderate	30,41,49
Time and location of the study	2	GRADE: N/A GRADE-CERQual: N/A	41,42
Physician recommendations/Referral	1	GRADE: N/A GRADE-CERQual: N/A	46
Research staff’s perspective
Physician recommendations/referral	4	GRADE: High GRADE-CERQual: N/A	28,40,46,51
Compensation/ incentives	2	GRADE: High GRADE-CERQual: N/A	37,50
Location of the study	1	GRADE: N/A GRADE-CERQual N/A	36

^aGRADE and GRADE-CERQual was done among themes with more than one study. N/A: not available because there were not enough studies of each type to evaluate certainty of the theme.

Benefits to others and self and nature of the intervention.

These two themes mentioned by parents and children were interrelated. Parents mentioned understanding the randomization process and the study’s success in explaining the process clearly as a facilitator.⁴² Additionally, parents and children expressed a desire to support science and to help find successful interventions for others in the future.^42,47 Children reported a willingness to participate due to a desire of changing their behaviors and building confidence and self-esteem²⁹ and that participating in the study would lead to a direct health benefit.^29,30,53 Parents also reported that programs improving parenting skills and getting ideas on how to change both physical activity and sedentary behaviors were motivating factors.⁴² Parents reported that they decided to participate in the study to make changes for their children and themselves,⁴⁸ and to improve the child’s overall “quality of life”.⁴⁵ Parents perceived that the intervention provided as part of their participation in the trial would enable changes in their child that could not otherwise be done at home.^47,48 The certainty in the evidence of these two themes was considered by GRADE as high and by GRADE- CERQual as moderate.

Compensation / Incentives.

Monetary compensation to promote participation in pediatric clinical trials may raise ethical questions and is regulated not only by federal/other agencies but also by institutional review boards (IRBs), with some prohibiting incentives of any nature for children, but evidence about this topic was very limited.⁵⁴ Monetary incentives served as a perceived facilitator reported by both groups.^{35,37,41,45,50} These incentives were found to be mainly cash or gift cards ranging from $5 to $50 per visit. One study provided as an incentive free child-care, which was reported as a facilitator.^31,42 The certainty in the evidence of this theme was considered by GRADE as high and by GRADE- CERQual as moderate.

Physician recommendations or referrals.

This was the main facilitator reported by researchers. In four studies,^28,40,46,51 referrals from health professionals, including school nurses, pediatricians, dieticians, among others, were the main recruitment method, accounting for more than 50% of the recruited sample. Parents reported that they enrolled because their physician recommended the study during their general pediatric appointment, or because they saw the flyer in the pediatric office, or because they received a letter from them.⁴⁶ The certainty in the evidence of this theme was considered by GRADE as high.

Support level.

If the parents showed interest and willingness to participate, the child was also more likely to join the study.⁴⁹ Children were also more likely to participate and stay involved if it allowed them to spend time with their peers.⁴¹ Besides, having support available from research staff made parents more willing to participate.³⁰ Parents mentioned receiving support when they missed a session and receiving reminders via text.⁴² Parents were also more likely to have their child participate if their friend was already signed up for the project and was motivated to learn from other parents.⁴² The certainty in the evidence of this theme was considered by GRADE as high.

Recruitment strategies

The most common recruitment strategies used in the studies included in the systematic review are shown in Table 8. Face-to-face recruitment was prevalent; this includes recruitment in the waiting area of medical offices, schools, clinics, etc. Healthcare provider referrals and partnering with clinics and/or public schools were very common too. Mailing letters or sending emails about the study to potential participants and using flyers were also common measures. Social media was only used in the most recent trials. Several studies reported having bilingual staff to recruit participants,^26,38,39,44 which may be important depending on the target population.

Table 8.

Recruitment strategies most used in the systematic review for children participation in nutrition, physical activity, and obesity interventions studies

Recruitment strategies	Number of studies	References
Face-to-face recruitment	7	36,38-40,42,44,46
Healthcare provider referrals	6	28,40,44,46,48,51
Partnering with communities (clinics and/or public schools)	6	26,38-41,44
Mailing letters and e-mails	5	25,28,39,46,51
Flyers	5	25,28,36,39,48
Social media	5	25,26,39,40,51
Repeated telephone calls and texts	5	28,38,41,44,51

Discussion

A variety of common themes were identified as barriers and facilitators of children's participation in nutrition, physical activity, and obesity interventions. Commonly reported barriers were time constraints, understanding of clinical trial information or complexity of consent/trial info, and transportation/lack of childcare. The most common facilitators were benefits to others and self, compensation/incentives, physician recommendations/referrals, and support.

Findings from this meta-summary were consistent with previously discussed systematic reviews assessing parental enrollment in preventative programs focused on children’s mental health¹⁶ and children enrollment into clinical trials related to chronic medical conditions and hypothetical drug trials.¹⁸ For example, Finan et al.¹⁶ observed higher enrollment rates when parents perceived the intervention to be beneficial for themselves as well as for their child if monetary compensation was offered, and when parents had support from family and friends. Similar motivating factors for recruitment were identified by Tromp et al.,¹⁸ which included personal health benefits, altruism, relationship with research staff, financial reimbursement, and influence of family/friends. Additionally, Tromp et al.,¹⁸ found similar barriers to recruitment as found in the present review, such as disruption of daily life, while Finan et al¹⁶ did not report discouraging factors for recruitment.

Frequently used recruitment strategies were also reported in this systematic review which included predominantly face-to-face recruitment, referrals from health care professionals, and partnering with local communities such as public schools and clinics, letters and emails, and flyers. Interestingly, Finan et al’s review reported these similar recruitment strategies for children’s mental health interventions.¹⁷ Surprisingly, only two studies mentioned the use of social media as a recruitment tool; however, most studies included in our review and other reviews were published several years ago before social media became a common tool. Given that social media has become a popular medium for information exchange, future research should explore the potential advantages and limitations associated with using social media for recruitment purposes.

Based on the information gathered in this systematic review, several recruitment methods can be utilized in future research that requires enrollment of children and parents for physical activity, nutrition, and childhood obesity interventions. Strategies to facilitate recruitment could expand on the use of social media and advertising the study on multiple platforms (e.g., Instagram, Facebook, Twitter, and LinkedIn); distributing emails and letters to target those that may not actively use social media; eliminating lack of time to participate in a study by offering the parent the option to complete questionnaires online before their visit; providing additional compensation to cover the cost of transportation to the study site; establishing relationships with healthcare staff and scheduling times to visit the recruitment site to build rapport with children and parents; developing educational webinars that pertain to the community’s interest, and providing clear and concise materials to facilitate the understanding about the study.

Strengths and Limitations

There were some limitations reported in the different studies when assessing the facilitators and barriers for both parents and children. Most parents and children interviewed were those that agreed to participate; therefore, their perspective may dominate the results. It is often difficult to reach those who decline participation to learn about the factors that hinder their willingness to enroll; therefore, there could be other barriers or facilitators that could be missing from the review. Only a few studies included the child’s perspectives. For them, having friends that were also part of the study was an important facilitator that was not identified by parents or researchers. By including older children, other themes could be identified. Lastly, most European trials did not disclose whether incentives or compensation were provided, while most of the trials in the US reported the amount given ($5-$50 per visit). Regulatory agencies and ethical committees may control pediatric trials’ compensation differently.

Our systematic review had some strengths and limitations that should also be mentioned. To our knowledge, this is the first systematic review that explores facilitators and barriers of recruiting children into nutrition, physical activity, and obesity interventions. Another strength was the inclusion of qualitative studies and mixed methods that allowed an in-depth perception of the barriers and facilitators. Other systematic reviews excluded qualitative studies^16,17 or only assessed these perceptions for drug trials.^16-19 Nevertheless, this review has a few limitations. Based on our inclusion and exclusion criteria, many trials were removed because they were drug trials or performed among children with chronic conditions, which limited the number of analyzed studies. Another limitation is that we were not able to include demographics because many studies did not evaluate this aspect. Therefore, it can be difficult in interpreting how these themes vary by ethnic or socioeconomic groups, which may lead to undiscovered themes. There was a wide range of measures used to evaluate the barriers and facilitators across the studies and assessment time points; some studies collected the data immediately after recruitment but others at the end of the study. This heterogeneity imposed an added challenge in interpreting the results.

Recommendations for future research

Future trials should include measures to evaluate the implementation of recruitment strategies from the start of the trial to timely reshape strategies (if recruitment is lagging) and to better inform future trials. These measures should be part of the protocol and implemented from the start. Within ethical parameters, future studies should aim to include older children when inquiring about recruitment barriers and facilitators.

Conclusions

This systematic review of qualitative and quantitative studies exploring barriers and facilitators for children’s participation in clinical trials related to nutrition, physical activity, and obesity interventions found that the most commonly reported barriers were time constraints, understanding of clinical trial information, or complexity of consent/trial info, and transportation/lack of childcare while the most common facilitators were benefits to others and self, compensation/incentives, physician recommendations/referrals, and support. These barriers could be addressed, in part, by designing interventions that incorporate components that could be implemented at home, such as the completion of online questionnaires, partnering with communication experts to reduce misunderstanding, and recruiting closer to the study site. The facilitators identified could be used as leverage in future studies to aid in the recruitment process.