幼い
おさない · osanai · JLPT N3 · i-adj
very young
👶🍼 osanai sounds like oh, so naive: what you say to someone very young
The kanji 幼 is 幺 (a tiny thread) + 力 (strength), so tiny strength means very young. Hook for the sound: osanai, oh so naive. It can describe a small child, or an adult who is behaving childishly.