Data from the U.S. National Longitudinal Survey of Youth 1979-90 are used to estimate relations between maternal age at first birth and measures of early socioemotional and cognitive development of children. Cross-sectional estimates are compared to estimates based on comparisons of first cousins to gauge the importance of bias from family background heterogeneity. Consistent with previous literature, cross-sectional estimates suggest adverse consequences of teenage motherhood for child development. However, children of teen mothers appear to score no worse on measures of development than their first cousins whose mothers had first births after their teen years. These findings suggest that differences in family background of mothers (factors that precede their childbearing years) may account for the low scores observed among young children of teen mothers. Issues such as these related to selection into teenage childbearing in the U.S. may be relevant for a variety of social settings and for domestic and international policy concerns.