picnic vs child's play

picnic and child's play both are nouns.

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

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

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

picnic (noun)	child's play (noun)
any undertaking that is easy to do	any undertaking that is easy to do
any informal meal eaten outside or on an excursion	activity by children that is guided more by imagination than by fixed rules
a day devoted to an outdoor social gathering

picnic (verb)	child's play (verb)
eat alfresco, in the open air