child vs yearling

child and yearling both are nouns.

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

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

child (noun)	yearling (noun)
a young person of either sex	an animal in its second year
a human offspring (son or daughter) of any age	a racehorse considered one year old until the second Jan. 1 following its birth
an immature childish person	a young child who is just beginning to walk
a member of a clan or tribe