The authors examined the effects of welfare programs that increased maternal employment and family income on the development of very young children using data from 5 random-assignment experiments. The children were 6 months to 3 years old when their mothers entered the programs; cognitive and behavioral outcomes were measured 2-5 years later. While there were no overall program impacts, positive or negative, on the development of children in this age group, there was a pair of domain- and age-specific effects: The programs decreased positive social behavior among 1-year-olds and increased school achievement among 2-year-olds. After exploring several explanations for these results, the authors suggest that the contextual changes engendered by the programs, including children's exposure to center-based child care, interacted differentially with specific developmental transitions.