The present study aimed to explore the mediating role of family-related determinants on the effects of the ToyBox-intervention on pre-school children’s consumption of healthy and unhealthy snacks.

The ToyBox-intervention was a kindergarten-based, family-involved intervention with a cluster-randomized design, aiming to promote healthy lifestyle behaviours to prevent obesity at pre-school age.

Kindergartens (n 309) in six European countries.

A total of 6290 pre-schoolers and their families participated in the ToyBox-intervention in 2012–2013 and data from 5212 pre-schoolers/families were included in the current analyses.

Even though the total effect of the ToyBox-intervention on healthy and unhealthy snacking was not significant, the ToyBox-intervention significantly improved parental rule setting on children’s unhealthy snack consumption (i.e. restriction of snacking while watching television and permission only at certain occasions) and parental consumption of unhealthy snacks, while it increased parental knowledge on snacking recommendations. Regarding healthy snacking, the ToyBox-intervention improved children’s attitude towards fruit and vegetables (F&V). All previously mentioned family-related determinants mediated the intervention effects on pre-schoolers’ consumption of healthy and unhealthy snacks. Almost all family-related determinants examined in the study were independently associated with pre-schoolers’ consumption of healthy and unhealthy snacks.

The intervention was effective in improving relevant family-related determinants. Interventions aiming to promote F&V consumption and limit the consumption of unhealthy snacks in pre-schoolers should target on these mediators, but also identify new family-, school- or peer-related determinants, to enhance their effectiveness.