This 3-arm RCT tests the effects of a sleep-enhanced adaptation (FF+) of a well-known, evidence-based transition-to-parenting coparenting intervention program (Family Foundations; FF). In one arm, families will experience FF as originally formulated; in the second, families will receive an adapted FF (FF+) program that emphasizes coparenting in infant sleep contexts; the third arm will serve as controls. It is hypothesized that (1) Compared to controls, parents in both FF groups will report improved overall coparenting and reduced overall distress, but parents in the FF+ group will show greater improvements in coparenting and individual parenting in infant sleep contexts, better infant and parent sleep, and better child adjustment; (2) early coparenting around infant sleep will be a central mechanism by which both interventions exert their effects.