You searched for: “childlike
childish, childlike
childish (CHIGHL dish) (adjective)
Suggesting a simplicity or immaturity befitting a very young person: Sidney had childish tantrums; especially, for a person who was working at the bank.
childlike (CHIGHLD lighk") (adjective)
Resembling behavior or attitudes compatible with the period of a person's life when he or she was very young: Faye had a childlike innocence about her that was appealing.

Fannie's nephew usually acted in a very childlike manner when he was visiting his grandmother; but when he threw a temper tantrum, it was more childish than usual.