child vs small fry

child and small fry both are nouns.

Word	Noun	Adjective	Verb	Adverb
child	Yes	No	No	No
small fry	Yes	No	No	No

As nouns, child and small fry are synonyms defined as:

Other synonyms of child include fry, kid, minor, nestling, nipper, shaver, tiddler, tike, tyke, youngster.

child (noun)	small fry (noun)
a young person of either sex	someone who is small and insignificant
a human offspring (son or daughter) of any age	a young person of either sex
an immature childish person
a member of a clan or tribe