Drawing on economic models of child development and attachment relationship perspectives, this study examined the effect of maternal employment in the first year after childbirth on subsequent behavioral and cognitive development in low-income children. Analyses of data from the Project on Human Development in Chicago Neighborhoods (N = 411) revealed that despite the accompanying family income gains, maternal employment in the first year after childbirth adversely affected caregiver-reported internalizing and externalizing behavior problems of Hispanic, Black, and White children at ages 3 and 5 years. This study also examined how paternal participation in childcare might affect children's outcomes. Results indicate that greater paternal participation eased the adverse impacts of maternal employment on internalizing behavior problems. There was no evidence that maternal employment was associated with children's memory cognitive functioning or that paternal involvement moderated children's cognitive development. These findings suggest that when early intervention programs are designed to assist low-income families, enhancing supports (e.g., paternal involvement or parental leave) for working mothers during their child's first year may be valuable for young children's healthy development.