babe vs blue baby

babe and blue baby both are nouns.

Word	Noun	Adjective	Verb	Adverb
babe	Yes	No	No	No
blue baby	Yes	No	No	No

As nouns, blue baby is a hyponym of babe; that is, blue baby is a word with a more specific, narrower meaning than babe:

babe: a very young child (birth to 1 year) who has not yet begun to walk or talk
blue baby: an infant born with a bluish color; usually has a defective heart

babe (noun)	blue baby (noun)
a very young child (birth to 1 year) who has not yet begun to walk or talk	an infant born with a bluish color; usually has a defective heart