child's game

NOUN
12 LETTERS · STARTS WITH C

child's game is a valid 12-letter word worth 19 points in Scrabble and 22 points in Words with Friends.

SCRABBLE WORDS WITH FRIENDS
C3H4I1L1D2'0S1G2A1M3E1
3 + 4 + 1 + 1 + 2 + 0 + 1 + 0 + 2 + 1 + 3 + 1 =19 PTS
DOUBLE WORD → 38TRIPLE WORD → 57
MEANING

What does child's game mean?