fosterling vs foster child

fosterling and foster child both are nouns.

Word	Noun	Adjective	Verb	Adverb
fosterling	Yes	No	No	No
foster child	Yes	No	No	No

As nouns, fosterling and foster child are synonyms defined as:

Other synonyms of fosterling include foster-child.

fosterling (noun)	foster child (noun)
a child who is raised by foster parents	a child who is raised by foster parents