female child vs female

female child and female both are nouns.

Word	Noun	Adjective	Verb	Adverb
female child	Yes	No	No	No
female	Yes	Yes	No	No

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

Other hypernyms of female child include female person.

female child (noun)	female (noun)
a youthful female person	an animal that produces gametes (ova) that can be fertilized by male gametes (spermatozoa)
	a person who belongs to the sex that can have babies

female child (adjective)	female (adjective)
	being the sex (of plant or animal) that produces fertilizable gametes (ova) from which offspring develop
	for or pertaining to or composed of women or girls
	characteristic of or peculiar to a woman