At the nexus of changing marital and fertility behavior is a new reality of contemporary family life—the fact that a significant fraction of adults today (will) have biological children by more than one partner, sometimes called ‘multi-partnered fertility.’ Among some disadvantaged groups, including unmarried parents and mothers on welfare, the majority of parents will have children with at least two partners, implying that their children will have one or more half-siblings and experience a complex family situation.

Multi-partnered fertility may have important implications for children’s wellbeing because it affects family roles, relationships and kinship networks, particularly concerning the rearing and socialization of children. When parents are called upon to provide resources to children across more than one household—or to children of different biological relatedness within the same household, the resulting complexities may compromise the quantity and/or quality of parental investment that children receive, potentially diminishing children’s well-being. Given that multi-partnered fertility disproportionately occurs to low-income and minority subgroups, this phenomenon may also contribute to social and economic inequality over time or, exacerbate the negative effects of growing up in economically-disadvantaged families

In this paper, we provide new evidence about how multi-partnered fertility is related to parental involvement and children’s well-being, comparing children whose mothers and/or fathers have a child by another partner to children with only full siblings. Using data from the Fragile Families and Child Wellbeing Study (that includes an over-sample of nonmarital births), we evaluate children’s cognitive and behavioral outcomes over ages 3, 5 and 9 as a function of various categories of multi-partnered fertility (and a host of covariates). We use random effects  models and fixed effects models to consider variation between and within different types of (non)complex families over time, and we use latent growth models to evaluate trajectories of child outcomes and the extent to which they are ‘disrupted’ by mothers or fathers having children by new partners.

Our preliminary results for pre-school-aged children suggest that fathers’ multi-partnered fertility is associated with lower paternal involvement with young children but has little effect on children’s outcomes, while mothers’ multi-partnered fertility is linked to greater externalizing behavioral problems and lower cognitive scores. This research has important implications for public policy: To the extent that many disadvantaged couples have children by more than one partner, the already-strained resources of low-income parents will by necessity spread across households, increasing the need for income supports and for programs to encourage strong parent-child ties.