juvenile vs nestling

juvenile and nestling both are nouns.

Word	Noun	Adjective	Verb	Adverb
juvenile	Yes	Yes	No	No
nestling	Yes	No	No	No

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

juvenile (noun)	nestling (noun)
a young person, not fully developed	young bird not yet fledged
	a young person of either sex

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