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