Background: Parents and peers are both likely to influence children’s dietary behaviour. However, their actual influence may depend on the age and life stage of the individual child. Therefore, this study examined the influence of parents (home snack availability and consumption rules) and peers on 11-year-old children’s snack consumption, and whether these associations were mediated by children’s snack-purchasing behaviour. It was hypothesized that children are more likely to buy unhealthy snacks if these are not always available at home, if restrictive rules apply to their consumption and if a child is sensitive to peer influence. It was also assumed that children who buy snacks out of their pocket money would consume more snacks. Methods: Data were taken from 1203 parent–child dyads who completed a questionnaire in the INPACT study (IVO Physical Activity Child cohorT). Multivariable regression models were used to (i) analyze associations between children’s consumption and parents’ and peers’ influence and (ii) determine whether these associations were mediated by children’s snack-purchasing behaviour. Results: Of the parental factors, home availability of snacks was associated with higher snack consumption (B = 1.03, P < 0.05). Parental factors and children’s snack-purchasing behaviour were not associated. Children who were sensitive to peer influence consumed more snacks (B = 3ċ07, P < 0.01) and bought more snacks out of their pocket money (odds ratio 3.27, P < 0.0.01). Children’s snack-purchasing behaviour explained part (8.6%) of the association between peer influence and children’s snack consumption. Conclusion: As these findings indicate that both parents and peers influence children’s snack consumption, health promotion may benefit from targeting the broader social environment.