wonder child vs small fry

wonder child and small fry both are nouns.

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

As nouns, small fry is a hypernym of wonder child; that is, small fry is a word with a broader meaning than wonder child:

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

wonder child (noun)	small fry (noun)
a prodigy whose talents are recognized at an early age	someone who is small and insignificant
	a young person of either sex