Archaic term for a very young child; not used in modern Japanese outside historical or literary contexts. Modern equivalents include 赤ちゃん or 幼児.
In old documents it is written as 孩児, but nowadays we say 赤ちゃん.
child
The exact derivation is uncertain; the spelling 孩児 is an archaic compound using kanji for 'infant' and 'child'.