kindergartener vs nestling

kindergartener and nestling both are nouns.

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

As nouns, nestling is a hypernym of kindergartener; that is, nestling is a word with a broader meaning than kindergartener:

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

kindergartener (noun)	nestling (noun)
a child who attends a preschool or kindergarten	young bird not yet fledged
	a young person of either sex