foster-child vs tyke

foster-child and tyke both are nouns.

Word	Noun	Adjective	Verb	Adverb
foster-child	Yes	No	No	No
tyke	Yes	No	No	No

As nouns, tyke is a hypernym of foster-child; that is, tyke is a word with a broader meaning than foster-child:

Other hypernyms of foster-child include child, fry, kid, minor, nestling, nipper, shaver, small fry, tiddler, tike, youngster.

foster-child (noun)	tyke (noun)
a child who is raised by foster parents	a young person of either sex
	a crude uncouth ill-bred person lacking culture or refinement