Zeinstra 2018.

Study characteristics
Methods	Study design: cluster‐RCT Length of follow‐up from baseline: 5 months Unit of allocation: centre Unit of analysis: child
Participants	Service type: centre‐based Operation: not reported Country (region): The Netherlands (Utrecht) Country income classification: high Low‐SES sample: unclear Population description: not reported Inclusion criteria: all 4 centres belonged to the same organisation. Healthy children without any allergies to the study products could participate. Exclusion criteria: not reported Number of services randomised: 4 (2 interventions, 2 control) Number of children randomised: 250 (125 intervention, 125 control) Characteristics Children Age: Intervention: 25.6 months (SD 9.6) Control: 25.0 (SD 10.2) Gender (% female): Intervention: 44% Control: 42% Ethnicity: not reported Parents Age (years): not reported Gender (% female): not reported Ethnicity: not reported Parent/family SES: Parent education level: Intervention: low: 0%; middle: 5%; high: 95% Control: low: 0%; middle: 10%; high: 90% Method of recruitment: information packs were distributed to 526 parents to inform them about the study aims and procedures. Missing data/dropout: not reported Reasons for dropout: not reported Characteristics of dropouts: not reported
Interventions	Programme name: not reported Number of conditions: 1 intervention, 1 control Intervention duration: 5 months (21 weeks) Intervention setting: ECEC Intervention strategies: Ethos and environment Children Exposure: each vegetable was served in 2 different preparations. Children were offered 1 vegetable product each day, in accordance with a predefined schedule. A vegetable song was played to make the vegetable eating occasion recognisable and fun for the children. The blanched and raw vegetables were offered on a group plate (portion available ~50 g/child). The spreads (~30 g) were offered on 1 or 2 crackers, and the soup was offered in an individual cup (~80 g). The children could eat as much or as little as they wanted from the vegetable products; child‐care employees invited the children to taste but never forced them to eat. ECEC staff Workshop: all ECEC employees were involved in a 1‐h workshop to explain the study procedures and to discuss and resolve any perceived barriers. Intensity of intervention: 1‐h ECEC staff workshop; children were offered 1 vegetable product each day. Intervention delivered by: research team, ECEC staff Modality: face‐to‐face Theoretical basis: not reported Description of control: usual care
Outcomes	Outcomes relating to child dietary intake: Pumpkin intake, white radish intake, courgette intake Number of participants analysed: not reported Data collection measure: research team weighed the vegetable cups before and after consumption; vegetable intake was calculated by subtracting the leftovers from the pre‐weight Data collector: researcher Validity of measures used: not reported Outcomes relating to child physical measures: not reported Outcome relating to child language and cognitive performance: not reported Outcome relating to child social/emotional measures: not reported Outcome relating to child quality of life: not reported Outcome relating to cost: not reported Outcome relating to adverse consequences: not reported
Notes	Funding source: The Fresh Produce Centre and the Ministry of Economic Affairs (grant number TU 1310‐086). Neither organization had any role in the design, analyses, or writing of this article.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	2 ECEC centres were randomly assigned to the intervention condition. The sequence generation procedure was not described.
Allocation concealment (selection bias)	Unclear risk	No information on the method of allocation concealment reported
Blinding of participants and personnel (performance bias) Diet outcomes	Unclear risk	All 4 ECEC centres were part of the same organisation, though the parents and day care employees were not informed about the exact study design and conditions until after the study ended. Study authors stated that "Employees were asked to refrain from making negative faces or negative comments regarding the food's smell, taste, texture, or appearance." However, they were not asked to refrain from encouragement, which could have increased children's intake. Further, "the childcare employees were instructed to maintain a neutral attitude, which may have been somewhat artificial."
Blinding of outcome assessment (detection bias) Diet outcomes	Low risk	Blinding of outcome assessors not reported, however children's consumption was measured by weighing the vegetable cups before and after intake out of the children's view. The outcome measurement is not likely to be influenced by lack of blinding.
Incomplete outcome data (attrition bias) Diet outcomes	Unclear risk	Study authors stated that "The final dataset contained 250 children." However, the number of children at baseline and follow‐up is not reported. Risk of attrition bias is unclear.
Selective reporting (reporting bias)	Unclear risk	No prospective trial protocol or trial registration so it was unclear whether there was selective outcome reporting
Recruitment bias	Unclear risk	It is unclear whether individuals were recruited to the study before or after randomisation of clusters.
Baseline imbalance	Low risk	There were no significant differences between the intervention and the control groups.
Loss of clusters	Unclear risk	Not reported
Incorrect analysis	Unclear risk	There was no accounting for clustering of children within centres, however all 4 centres were part of the same organisation. There is not enough information to assess whether an important risk of bias exists.
Contamination	Unclear risk	All 4 centres were from the same community and belonged to the same organisation. However, this is unlikely to have affected the intervention given the nature of the intervention (repeated exposure to unfamiliar vegetables in the child‐care centre).
Other bias	Unclear risk	Discrepancies are noted in the manuscript regarding what teachers were instructed to do (or not do) during pretest and post‐test. There is insufficient information to assess whether an important risk of bias exists. The intervention received financial support from a commercial organisation. Study authors state that this company had no operational role.

CDC: Centres for Disease Control; ECEC: early childhood education and care; FFQ: Food Frequency Questionnaire; GED: General Educational Development (tests); IOTF: International Obesity Task Force; ITT: intention‐to‐treat; PedsQL: Pediatric Quality of Life Inventory; RCT: randomised controlled trial; SD: standard deviation; SE: standard error; SES: socioeconomic status; USDA: United States Department of Agriculture; WHO: World Health Organization