Using a large sample from the National Institute of Child Health and Development Study of Early Child Care and Youth Development (N = 1,178, 51% were male and 80% were White), the random intercept cross-lagged panel model was employed to unpack the trait and state aspects in the relations between mothers’ depressive symptoms and children’s behavioral problems from age 2 to 15. The transactional predictions among mothers’ depressive symptoms and children’s behavioral problems were largely attributed to their correlations at the underlying trait level (rs = .458–.528). At the state level, the mutual influences among mothers’ depressive symptoms and children’s behavior problems occurred more often during periods of transition. With that said, the child effects hypothesis was not supported.