Using quantitative data from the Fragile Families and Child Wellbeing Study, as well as qualitative data from an in-depth study of low-income fathers in Philadelphia, this chapter describes the characteristics of young adults who transition to parenthood before 25 and the family contexts into which their children are born. Most births to young adults occur outside of marriage, but unmarried parents typically rally around the birth of their child, claiming a commitment to making their relationships work. Yet, the responsibility of providing for a family of their own before they have achieved financial stability proves to be an enormous strain for most. Perhaps because the children of young adults are seldom explicitly planned, and because economic hardship and parenthood strain even the most committed relationships, young parents break up at higher rates than couples who delay childbearing. Young parents who break up with their partners do not remain single for very long, however, and quickly enter into new romantic relationships, many of which produce additional children. The churning of romantic partners, and the birth of additional children who result, create a complex web of economic obligations and negotiations that complicate paternal access to nonresident children, compromise maternal parenting, and create unstable family environments for young children.