Although the emotional side of development was overshadowed by cognition for several decades, new excitement surrounds the study of emotions today. The functionalist approach emphasizes that the broad function of emotions is to prompt action in the service of personal goals. It regards emotions as central forces in all aspects of human activity--cognitive processing, social behavior, and even physical health--and as becoming increasingly voluntary and socialized with age.

The development of emotional expression is a gradual process that begins in infancy and continues into adolescence. Changes in happiness, anger, sadness, and fear reflect infants' developing cognitive capacities and serve social as well as survival functions. Signs of almost all the basic emotions are present in early infancy, and they soon become clear, well-organized signals. At the end of the second year, self-conscious emotions emerge. Emotional self-regulation begins in infancy, and during the preschool years, children start to conform to the emotional display rules of their culture. Parenting practices and the child's temperament affect the development of emotional self-regulation. The ability to meaningfully interpret others' emotional expressions emerges at the end of the first year. Around this time, infants start to engage in social referencing. Although the roots of empathy are present early in development, true empathy requires children to understand that the self is distinct from other people.

Heredity influences early temperament, but child-rearing experiences affect whether a child's emotional style is sustained or modified over time. According to ethological theory, infants are biologically prepared to contribute to the attachment bond with the caregiver, which evolved to promote survival. Caregiving that is responsive to babies' needs supports the development of secure attachment; insensitive caregiving is linked to attachment insecurity. Family conditions, parents' internal working models, and infants' health and temperament also contribute to quality of attachment. Although some findings indicate that secure attachment in infancy causes improved cognitive, emotional, and social competence during later years, continuity of caregiving may be responsible for these outcomes.

Today the majority of American mothers with children younger than age 2 are employed. Infant child care is associated with a slight risk of attachment insecurity. Quality of care is the determining factor in the effect of child care on young children's emotional security.