war baby vs infant

war baby and infant both are nouns.

Word	Noun	Adjective	Verb	Adverb
war baby	Yes	No	No	No
infant	Yes	No	No	No

As nouns, infant is a hypernym of war baby; that is, infant is a word with a broader meaning than war baby:

war baby: conceived or born during war
infant: a very young child (birth to 1 year) who has not yet begun to walk or talk

Other hypernyms of war baby include babe, baby.

war baby (noun)	infant (noun)
conceived or born during war	a very young child (birth to 1 year) who has not yet begun to walk or talk