juvenile vs small fry

juvenile and small fry both are nouns.

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

As nouns, small fry is a hyponym of juvenile; that is, small fry is a word with a more specific, narrower meaning than juvenile:

juvenile (noun)	small fry (noun)
a young person, not fully developed	someone who is small and insignificant
	a young person of either sex

juvenile (adjective)	small fry (adjective)
of or relating to or characteristic of or appropriate for children or young people
displaying or suggesting a lack of maturity