We investigate the impact of maternity leave on the cognitive and behavioral development of children at ages 4 and 5. The impact is identified by legislated increases in the duration of maternity leave in Canada, which significantly increased the amount of maternal care children received in the second half of their first year. We carefully document how other observable inputs to child development vary across cohorts of children exposed to different maternity leave regimes. Our results indicate that maternity leave changes had no positive effect on indices of children's cognitive and behavioral development. We uncover a small negative impact on PPVT and Who Am I? scores, which suggests the timing of the mother/child separation due to the mother's return to work may be important.