Objective There is limited understanding as to why children of low socio-economic position (SEP) consume poorer diets than children of high SEP. Evidence suggests that determinants of dietary intake may differ between SEP groups. The present study aimed to determine if SEP moderated associations of personal and environmental predictors with children's non-core food and sweetened drink intakes and unhealthy dietary behaviours. Design Children completed online questionnaires and parents completed computer-assisted telephone interviews to assess intrapersonal and environmental dietary predictors. Dietary intake was measured using an FFQ. Parents reported demographic information for maternal education, occupation and employment, and household income. Setting Twenty-six primary schools in South Australia, Australia. Subjects Children aged 9-13 years and their parents (n 395). Results Multiple personal and home environment factors predicted non-core food and sweetened drink intakes, and these associations were moderated by SEP. Maternal education moderated associations of girls' sweetened drink intake with self-efficacy, cooking skills and pressure to eat, and boys' non-core food intake with monitoring, parent's self-efficacy and home environment. Maternal occupation and employment moderated associations of sweetened drink intake with attitudes, self-efficacy, pressure to eat and food availability, and non-core food intake with parents' self-efficacy and monitoring. Income moderated associations with pressure to eat and home environment. Conclusions Identifying differences in dietary predictors between socio-economic groups informs understanding of why socio-economic gradients in dietary intake may occur. Tailoring interventions and health promotion to the particular needs of socio-economically disadvantaged children may produce more successful outcomes and reduce socio-economic disparities in dietary intake.