fosterling vs youngster

fosterling and youngster both are nouns.

Word	Noun	Adjective	Verb	Adverb
fosterling	Yes	No	No	No
youngster	Yes	No	No	No

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

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

fosterling (noun)	youngster (noun)
a child who is raised by foster parents	a young person of either sex