childish

It was childish of him to stop speaking to his friend just because of a small argument.

(Chinese) 仅仅因为一点小争吵就跟朋友绝交，他这种做法太幼稚了。

She was tired of her brother's childish practical jokes that often caused a mess.

(Chinese) 她讨厌哥哥那些经常把事情搞得一团糟的幼稚恶作剧。