This article develops and estimates a dynamic model of employment and child care decisions of women after childbirth to evaluate the effects of these choices on children's cognitive ability. We use data from the National Longitudinal Survey of Youth to estimate it. Results indicate that the effects of maternal employment and child care on children's ability are negative and sizable. Having a mother that works full-time and uses child care during one year is associated with a reduction in ability test scores of approximately 1.8% (0.13 standard deviations). We assess the impact of policies related to parental leave and child care on children's outcomes.