This report investigates the effects of maternal employment on child development. It compares data from countries with different types of work-family policy - Australia, Canada, Denmark, the United Kingdom, and the United States - using data from national birth cohort studies, including the Longitudinal Study of Australian Children (LSAC), the National Longitudinal Survey of Children and Youth (NLSCY) from Canada, the Danish Longitudinal Survey of Children (DALSC), the Millennium Cohort Study (MCS) from the UK, and the Early Childhood Longitudinal Study (ECLS) from the US. The report compares children's behavioural and cognitive outcomes, the timing and intensity of maternal employment, child care arrangements, and family characteristics. The findings suggests that a return to paid work by mothers within six months after childbirth may have negative effects on child outcomes, but the effects are small and not universally observed. Other factors such as family income, parental education and quality of interaction with children were found to have greater effects on development.