child prodigy vs youngster

child prodigy and youngster both are nouns.

Word	Noun	Adjective	Verb	Adverb
child prodigy	Yes	No	No	No
youngster	Yes	No	No	No

As nouns, youngster is a hypernym of child prodigy; that is, youngster is a word with a broader meaning than child prodigy:

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

child prodigy (noun)	youngster (noun)
a prodigy whose talents are recognized at an early age	a young person of either sex