Social-Emotional Development: Social-emotional development includes children’s growing abilities to form relationships, interact with peers and adults, express emotions, respond to other people’s feelings, participate in groups, and gradually regulate emotions and behavior. Cooperative play, responsive caregiving, predictable routines, and supportive adult-child relationships provide everyday opportunities to practice these abilities. CDC milestones include behaviors such as noticing other children, joining them in play, taking turns, and comforting others.