**Background:** Childhood obesity is a global public health concern, with rapid weight gain occurring between ages 2 and 6. The Melbourne Infant, Feeding, Activity and Nutrition Trial (INFANT) was a community-based cluster-randomized controlled trial (2008–2010) targeting first-time Australian parents of infants aged 4 months. Post-intervention (15 months), children in the intervention group consumed significantly less sweet snacks and watched less television. At long-term follow-ups (2 and 3.5 years post-intervention), sustained positive effects were observed for fruit, vegetable, sweet snack, and water intake at 2 years, and for non-core drinks and sweet snacks at 3.5 years; television viewing was about 10 minutes less per day at both time points. Maternal education and age are known predictors of child BMI and dietary patterns, but few studies have examined whether these factors moderate long-term intervention effects. This study aimed to assess whether the effectiveness of INFANT varied by maternal education and age at 2 and 3.5 years post-intervention.
**Methods:** INFANT randomized 542 children; 492 (91%) completed the 15-month program. All 492 families were invited to follow-ups when children were 3.6 and 5 years old. At the 2- and 3.5-year follow-ups, 358 and 362 children had outcome data, respectively. Outcomes included BMI z-scores (using WHO growth charts), total physical activity (ActiGraph accelerometer, ≥4 days with ≥7.4 h/day wear time), television viewing (parental report, two questions on weekday/weekend), and dietary intake (three multi-pass 24-hour dietary recalls). Maternal education was dichotomized as university degree vs. no university degree; maternal age was dichotomized at the median (32 years). Random effects linear regression models with bootstrapped standard errors (2000 re-samples) were used, including interaction terms (maternal education/age × intervention group). A P-value of 0.2 was used to indicate significance for moderation analyses. Stratified analyses were conducted using linear combinations post-estimation.
**Key Results:** At the 2-year follow-up, maternal education moderated the intervention effect for vegetable intake (interaction P=0.090), water intake (interaction P=0.076), and sweet snack intake (interaction P=0.079). Children of university-educated mothers in the intervention group consumed 30.26 g/d more vegetables (95% CI 11.03, 49.50) and 9.30 g/d less sweet snacks (95% CI –14.82, –3.79) compared to controls. Children of non-university-educated mothers in the intervention group consumed 184.63 g/d more water (95% CI 47.31, 321.94). At the 3.5-year follow-up, maternal education moderated BMI z-score (interaction P=0.126) and water intake (interaction P<0.001), but stratified analyses showed no significant differences; however, a trend for greater water intake in children of non-university-educated mothers persisted (+114.28 g/d, 95% CI –38.75, 267.31).
For maternal age at the 2-year follow-up, moderation was observed for water intake (interaction P=0.052), sweet snack intake (interaction P=0.075), and physical activity (interaction P=0.110). Children of younger mothers (<32 years) in the intervention group consumed 177.36 g/d more water (95% CI 80.54, 274.19); children of older mothers (≥32 years) consumed 9.91 g/d less sweet snacks (95% CI –15.65, –4.17). No significant intervention effect for physical activity was found in either subgroup. At the 3.5-year follow-up, maternal age moderated fruit intake (interaction P=0.046), sweet snack intake (interaction P=0.136), savoury snack intake (interaction P=0.003), and physical activity (interaction P=0.200). Children of younger mothers in the intervention group consumed 11.54 g/d less sweet snacks (95% CI –20.57, –2.52) but 5.56 g/d more savoury snacks (95% CI 0.70, 10.41); children of older mothers consumed 5.15 g/d less savoury snacks (95% CI –9.48, –0.81). Trends for fruit intake and physical activity were not statistically significant.
**Clinical Implications:** The study found that INFANT was largely equally effective across different levels of maternal education and age, with only a few inconsistent moderating effects. This suggests that community-based interventions like INFANT can be broadly applied without major differential effects by socioeconomic or age subgroups. The positive effects on water intake in lower-educated mothers and on vegetable/sweet snack intake in higher-educated mothers at 2 years highlight potential areas for targeted support. However, the lack of sustained moderation at 3.5 years indicates that booster sessions or ongoing support may be needed to maintain differential benefits. The findings support the use of universal interventions in early childhood obesity prevention, while acknowledging that some subgroups may require additional strategies to achieve optimal outcomes.