This paper uses data from the National Longitudinal Survey of Youth to explore links between mothers' returns to work within 12 weeks of giving birth and health and developmental outcomes for their children. OLS models and propensity score matching methods are utilised to account for selection bias. Considerable associations between early returns to work and children's outcomes are found suggesting causal relationships between early returns to work and reductions in breastfeeding and immunisations, as well as increases in externalising behaviour problems. These results are generally stronger for mothers who return to work full-time within 12 weeks of giving birth.