OBJECTIVE: Strong social inequalities exist in chronic diseases related to diet and lifestyle. However, few studies have comprehensively examined the social determinants of children's diet at the family level, including paternal characteristics and migration background. This study aimed to assess the associations between family-based socio-ecological factors and children's dietary patterns (DP) during the first 2 years of life. DESIGN: This longitudinal observational study applied a socio-ecological model to explore associations with children's DP. We conducted multivariable linear regression analyses with DP - identified via principal component analysis - as outcomes, sequentially adjusting for maternal factors: immigrant status, education, older children in the household, single motherhood and age (block 1); occupation (block 2) and household income (block 3). Similar analyses were performed with paternal characteristics. SETTING: Nationwide French ELFE birth cohort. PARTICIPANTS: We used data from an FFQ completed by parents of 12 696 2-year-old children. RESULTS: Children born to mothers with a low socio-economic position (low education level; manual worker, unemployed or student or in the lowest household income quintile), with previous children, or who were living as a single parent had low scores on a DP defined as 'Balanced and diversified'. These children also showed greater adherence to a 'Discretionary consumption' pattern, as did those born to immigrant mothers. Overall, consistent findings were observed with paternal socio-economic factors. CONCLUSIONS: Early-life dietary inequalities are shaped by family-level social determinants, emphasising the need for early nutritional interventions tailored to disadvantaged families, particularly those with a migration background, low socio-economic status or single parenthood.