Playful, affectionate, or teasing term for a child, often used by adults when speaking to or about young children. Can sound slightly condescending if used for older kids.
This movie is too early for little kids.
childish person; immature person
Used teasingly or critically for an adult who acts like a child. Often light-hearted but can be mildly insulting.
He sulks right away, so he's still a child.
Thank you for taking care of my little one.
Getting mad over something like that—what are you, a kid?
A playful coinage from お子 (child) + ちゃま, a baby-talk or affectionate variant of さま (honorific). The exact origin is uncertain, but it likely emerged in casual, child-directed speech.