young (having lived or existed for only a short time; not old): young children/animals/trees
teenage (between 13 and 19 of age): We have two teenage children.
teen American informal (teenage): He is too old now for teen parties.
juvenile (relating to young people): Juvenile crime is increasing at a very high rate.
junior (relating to young or younger people): The national junior swimming championship will begin next month.
adolescent (of the age when a child is changing into an adult): Parents usually find it hard to understand their adolescent children.