sonny boy vs laddie

sonny boy and laddie both are nouns.

Word	Noun	Adjective	Verb	Adverb
sonny boy	Yes	No	No	No
laddie	Yes	No	No	No

As nouns, sonny boy and laddie are synonyms defined as:

sonny boy and laddie: a male child (a familiar term of address to a boy)

Other synonyms of sonny boy include cub, lad, sonny.

sonny boy (noun)	laddie (noun)
a male child (a familiar term of address to a boy)	a male child (a familiar term of address to a boy)