A child is a young person who's typically older than a baby but younger than a teen. As a child, you probably had your parents watching over you as you played in a sandbox.
The noun child come from the Old English word cild, meaning "child, infant." Retaining a similar meaning into modern times, the word still refers to a young person, male or female. But you can be considered a child after reaching adulthood — in the eyes of your parents, at least. Immature behavior like throwing a temper tantrum can also mark you as a child. The word can also refer to someone in a clan or tribe, young or old.