foundling vs infant

foundling and infant both are nouns.

Word	Noun	Adjective	Verb	Adverb
foundling	Yes	No	No	No
infant	Yes	No	No	No

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

foundling: a child who has been abandoned and whose parents are unknown
infant: a very young child (birth to 1 year) who has not yet begun to walk or talk

Other hypernyms of foundling include babe, baby.

foundling (noun)	infant (noun)
a child who has been abandoned and whose parents are unknown	a very young child (birth to 1 year) who has not yet begun to walk or talk