child vs infant

child and infant both are nouns.

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

As nouns, infant is a hyponym of child; that is, infant is a word with a more specific, narrower meaning than child:

child: a human offspring (son or daughter) of any age
infant: a very young child (birth to 1 year) who has not yet begun to walk or talk

Other hyponyms of child include army brat, babe, baby, female offspring, male offspring, man-child, stepchild.

child (noun)	infant (noun)
a young person of either sex	a very young child (birth to 1 year) who has not yet begun to walk or talk
a human offspring (son or daughter) of any age
an immature childish person
a member of a clan or tribe