Table 1. Study inclusion criteria.

Design	Randomised, and quasi-randomised, controlled trials, including individual cluster randomised trials
Participants	Studies which targeted pregnant women and/or parents (including mothers/fathers/carers/guardians) of healthy infants less than two years old and/or infants born at term gestation (37 to 42 weeks of gestation) and up to two years of age. ○  No restrictions for sex, ethnicity, socio-economic group, or region, were applied. ○  Studies where children aged under two years were part of a family group receiving the intervention were included only if data could be extracted separately for these children
Intervention	○  Behavioural interventions designed to prevent obesity (by directly/explicitly focusing on childhood obesity prevention, or by indirectly focusing on childhood obesity-related risk factors) in infants (e.g. individual counselling, face-to-face sessions, audio-visual packages, support groups, online interventions/forums) delivered by health professionals antenatally and/or up to a child's second birthday. ○  Behavioural interventions were defined as “those that require the active participation of a target group (e.g. patient, individual, health professional) in a programme delivered by a trained interventionist with the goal of changing health- related behaviour” 37. ○  Interventions targeting key risk factors for childhood obesity 38, including: early rapid weight gain, infant feeding method, timing of introduction of solid foods, and gestational weight gain ○  Health professionals were defined according to the International Standard Classification of Occupations (ISCO) ISCO- 08 39. For the purposes of this review, research nurses, lactation consultants, psychologists, and social workers were also classified as health professionals
Comparator	Participants who were not exposed to an intervention/wait-list control, or an active comparator, or who received 'usual care'. ‘Usual care’ is defined as standard support and/or appointments without an obesity prevention focus
Outcomes	Primary ○  Infant/child body mass index (BMI) z score ○  Additional anthropometric/growth-related: e.g. growth rates (weight gain, linear growth, and head growth, change in BMI z score), percent fat content, ponderal index, skin-fold thickness Secondary (*intermediate behavioural outcomes) ○  Diet-related*: e.g. breastfeeding initiation and duration (total and exclusive); dietary intake and quality; timing of introduction of solid food(s) ○  Feeding/eating behaviour-related*: e.g. responsive feeding practices ○  Physical activity-related*: e.g. physical activity, tummy time, play, screen time ○  Sedentary time/behaviour-related*: e.g. frequency/time spent: being inactive, doing specific low-energy behaviours such as screen time ○  Sleep* ○  Environment-related*: e.g. outcomes related to the physical (e.g. food availability) and social environment ○  Cost effectiveness/costs of the intervention
Publications	Trials reported only as abstracts were deemed eligible for inclusion if sufficient information was available from the report, or from contact with the authors, to fulfil the inclusion criteria