child vs somebody

child and somebody both are nouns.

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

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

child: an immature childish person
somebody: a human being; person, singular, assertive existential pronoun; pronoun, person, singular; quantifier: assertive existential

Other hypernyms of child include individual, mortal, person, someone, soul.

child (noun)	somebody (noun)
a young person of either sex	a human being; person, singular, assertive existential pronoun; pronoun, person, singular; quantifier: assertive existential
a human offspring (son or daughter) of any age
an immature childish person
a member of a clan or tribe