Maternal depression is a robust risk factor for children's internalizing symptoms; however, the intergenerational transmission of mood disorders is likely more complex than unidirectional parent-directed effects. Theoretical models support transactional associations between maternal and child symptomatology over time but have not been well examined, especially in younger high-risk samples. The present investigation examined predictive transactional relations between maternal depression and children's internalizing in toddlerhood and early childhood using a cross-lagged panel model. Participants were 162 low-income, largely racial/ethnic minority mothers and their offspring (32% African American, 16% White, 52% Other/Multiethnic; 53% female) who were assessed when children were 18 months and 4 years old. There were significant cross-sectional relations between maternal depressive and child internalizing symptoms when children were 18 months but not 4 years of age. Cross-lagged associations were evident such that maternal depression symptoms at 18 months were positively associated with internalizing symptoms among children at 4 years, adjusting for prior maternal symptom levels and the cross-sectional correlations between maternal-child symptoms at 18 months. Within the same model, children's internalizing symptoms at 18 months were also positively associated with maternal depressive symptoms at 4 years, adjusting for prior child symptom levels and cross-sectional correlations. This study is among the first to demonstrate that transactional relations between maternal and child mood symptoms occur as early as toddlerhood/early childhood. Findings highlight the potential utility of inclusive, family-focused interventions that support both parents and children in the treatment of early emotional problems.