street child vs nipper

street child and nipper both are nouns.

Word	Noun	Adjective	Verb	Adverb
street child	Yes	No	No	No
nipper	Yes	No	No	No

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

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

street child (noun)	nipper (noun)
a homeless child especially one forsaken or orphaned	a grasping structure on the limb of a crustacean or other arthropods
	a young person of either sex