幼稚な子供たちにも分かるように、絵を使って説明した。
I used pictures to explain it so that even very young children could understand.
まだ幼稚な弟の面倒を見るのは姉の役目だった。
Looking after her little brother, who was still very young, was the older sister's job.
幼稚な者を相手に本気で腹を立てるものではない。
You shouldn't get truly angry at someone so young.