The prevalence of child marriage in West Africa is one of the highest in the global south. Yet, much of what we know about the harmful effects of early marriage and why it persists comes from research on South Asia. Adopting life course family development perspectives on adolescent sexuality, we examine the linkages between the timing of union formation and childbearing across multiple countries with high rates of child marriage. Using the latest round of data from the Demographic and Health Surveys (DHS), we find that by age 18, 28 percent of adolescents in Nigeria, 25 percent in Burkina Faso, and as high as 60 percent in Niger are in a union, whilst 13 percent of Nigerian adolescents, 12 percent in Burkina Faso, and 27 percent in Niger have had a first birth. The results demonstrate that, net of individual characteristics, community variables are strong predictors of union formation and childbearing. Individual characteristics such as women's education, economic status of households, and residing in female-headed households and rural areas are other salient determinants of adolescent family transitions. We discuss the findings in the context of revamping stalled fertility transitions and the post-2015 framework for development in sub-Saharan Africa.