The recent establishment of two national, longitudinal studies of contemporary birth cohorts in the UK and USA creates a valuable opportunity for cross‐national research on the experiences of young children and their families. This article describes these new datasets and highlights the potential advantages and challenges of their combined use. To illustrate some of the issues involved in comparative research, we describe our study of the patterns and predictors of UK and US mothers’ (re)entry into the labour force during infants’ first 9 months of life. Similar to previous studies, we find that US mothers engage in paid work much sooner after childbirth than UK mothers. In both samples, greater financial and human capital predict higher rates (and earlier entries) of post‐birth employment; however, among the subset of US mothers who were employed pre‐birth, it is socioeconomic disadvantage that predicts sooner returns. We consider how different policy environments in the UK and USA help to explain these findings, and discuss directions for future research with these data