puerile

他在重要场合表现得如此幼稚，真是让人失望。

His ___puerile behavior at the formal event was truly disappointing.

他把办公室打印机的纸盒藏起来当恶作剧，这种幼稚的行为让他收到了正式警告。

His ___puerile decision to hide the office printer's paper tray as a joke earned him a formal reprimand.

两个成年兄弟为最后一个饺子发生了幼稚的争吵，之后各自默默吃饭谁也不理谁。

The two grown brothers ate their food in silence after a ___puerile squabble over the last dumpling.