The establishment of early bedtime routine is essential for children's emotion and behavioral outcomes. Less is known, however, about the longitudinal effects and mechanisms predicting behavioral outcomes through early bedtime routine and emotion regulation in school-age children from low-income families. Thus, the present study examined emotion regulation at age three as a potential mediator in the longitudinal links between early bedtime routine and behavioral outcomes among racially diverse school age children from low-income families. Participants include a subsample of families (n = 2977) participating in the Early Head Start Research and Evaluation Project (EHSRE). Structural equation modeling with bootstrapping techniques was used to examine the models. The early bedtime routine index was created from parents' reports at 14, 24, and 36 months. Children's emotion regulation was drawn from interviewer assessments at 36 months and problem behaviors were reported by mothers when the child was approximately at age 10. Results indicated that children with consistent early bedtime routine were better able to regulate their emotions at age three. Also, emotion regulation at age three mediated the associations between early bedtime routine at 14-36 months and internalizing and externalizing behaviors among fifth-grade children. Findings indicated that consistent early bedtime routine helps children to regulate their emerging emotions which in turn has long-term benefits on their emotional and behavioral outcomes. These findings have important implications for pediatricians, nurse practitioners, nurses, and early childhood educators who can provide education and resources to support families in establishing consistent bedtime routine for their young children.