Childhood (being a child)'s a broad term usually applied to the phase of development in humans between infancy and adulthood. Age definition of a child In many countries there's an age of majority when childhood ends and a person legally becomes an adult. The age can range anywhere from 13 to 21, with 18 being the most common. Research in social sciences In recent years there's been a rapid growth of interest in the sociological study of adulthood. Reaching on a large body of contemporary soci… (More on Childhood)