The study of the emotional development of infants and children is relatively new, having been studied empirically only during the past few decades. Researchers have approached this area from a variety of theoretical perspectives, which differ mainly on the question of whether emotions are learned or biologically predetermined.

Between six and ten weeks, a social smile emerges, usually accompanied by other pleasure-indicative actions and sounds, including cooing and mouthing. This social smile occurs in response to adult smiles and interactions. As infants become more aware of their environment, smiling occurs in response to a wider variety of contexts. Smiles are considered to serve a developmental function.

Laughter, which begins at around three or four months, requires a level of cognitive development because it demonstrates that the child can recognize incongruity. That is, laughter is usually elicited by actions that deviate from the norm, such as being...