Using a representative sample of children all born to unwed parents drawn from the Fragile Families and Child Wellbeing Study and a potential outcome approach to account for self-selection into marriage, we investigate whether marriage after childbearing has a causal effect on early child development. Comparing children with similar background characteristics and parental mate-selection patterns who differ only in terms of whether their parents marry after childbirth, we find that marriage after childbirth significantly increases a child's early cognitive performance but there is no evidence that it affects child asthma risk or behavioral outcomes.