A child is a human between the stages of birth and puberty. The legal definition of child generally refers to a minor, otherwise known as a person younger than the age of majority. In U.S. Immigration Law, a child refers to anyone who is under the age of 21. Every child goes through many stages of social development. An infant or very young child will play alone happily. If another child wanders onto the scene, he or she may be physically attacked or pushed out of the way. Next, the child can play with another child, gradually learning to share and take turns. Eventually, the group grows larger, to three or four children. By the time a child enters kindergarten, he or she can usually join in and enjoy group experiences.