Synonyms for Half-pint:

adj.

puny (adjective)
shrimp, peewee.

n.

boy (noun)
runt.
half-pint (noun)
peewee, runt, shrimp.
person (noun)
peewee, runt, shrimp.

Other synonyms:

adj.
peewee, shrimp.
n.
runt.