cinch vs child's play

cinch and child's play both are nouns.

Word	Noun	Adjective	Verb	Adverb
cinch	Yes	No	Yes	No
child's play	Yes	No	No	No

As nouns, cinch and child's play are synonyms defined as:

Other synonyms of cinch include breeze, duck soup, picnic, piece of cake, pushover, snap, walkover.

cinch (noun)	child's play (noun)
a form of all fours in which the players bid for the privilege of naming trumps	any undertaking that is easy to do
any undertaking that is easy to do	activity by children that is guided more by imagination than by fixed rules
stable gear consisting of a band around a horse's belly that holds the saddle in place