We draw on three waves of the Fragile Families Study (N = 2,249) to examine family stability among a recent birth cohort of children. We find that children born to cohabiting versus married parents have over five times the risk of experiencing their parents' separation. This difference in union stability is greatest for White children, as compared with Black or Mexican American children. For White children, differences in parents' education levels, paternal substance abuse, and prior marriage and children account for the higher instability faced by those born to cohabiting parents, whereas differences in union stability are not fully explained among Black and Mexican American children. These findings have implications for policies aimed at promoting family stability and reducing inequality.