Pictograph of a child (人) with an opening in the top of its head (囟). Represents the soft spot (fontanel) at the top of young infant heads. The 囟 component is written like 臼.
Shuowen Jiezi
《說文》：“兒，孺子也。从儿，象小兒頭囟未合。”
Components
囟(iconic) — Depicts the gap between the bones in an infant skull.