This document discusses emotional development from infancy through adolescence. It notes that emotional development progresses along with physical and cognitive development from birth. While emotions are difficult to study, researchers have developed theories of emotional development. The document then outlines key milestones in emotional development at different ages, including the emergence of smiling, crying, laughter, and other emotions in infancy, and the development of self-awareness, empathy, and emotional regulation in toddlerhood and childhood. It discusses challenges with emotional expression and understanding among adolescents.