childish
adj.adj. behaving like a child in a way that is annoying or silly. You use this when an adult acts immaturely or lacks self-control.
adj. characteristic of a child, especially in a negative sense such as immaturity or lack of emotional control. Often carries a pejorative tone when applied to adults.
His childish behavior during the meeting was very unprofessional.
It was childish of him to stop speaking to his friend just because they had a small disagreement.
While some found his enthusiasm charming, others dismissed his refusal to engage with the serious aspects of the proposal as merely childish and obstructive.
From Middle English childisch, from Old English ċildisċ. By surface analysis, child + ish.
Typically used as a critical descriptor for adults; 'childlike' is the positive alternative for innocent or pure qualities.
He has a childish smileHe has a childlike smile'Childish' is usually an insult meaning immature; 'childlike' is a compliment meaning innocent or sweet.