kindergartner vs small fry

kindergartner and small fry both are nouns.

Word	Noun	Adjective	Verb	Adverb
kindergartner	Yes	No	No	No
small fry	Yes	No	No	No

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

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

kindergartner (noun)	small fry (noun)
a child who attends a preschool or kindergarten	someone who is small and insignificant
	a young person of either sex