According to pseudo-Apollodorius, they were the Korybantes, but since they were worshippers of Cybele (Rhea) that seems unlikely.

Yes, Apollo had many children. His immortal children included :

Asklepios, god & prince of Messenia

Aristaios, rustic god

Korybantes Samothrakioi, demi-gods of the Mysteries

Skylla, sea monster of straits of Messina

Zeus, Hades and Poseidon are the sons of Cronus and Rhea.

Chiron, Aphros and Dolops are the sons of Cronus and Philyra.

Aphros and Bythos are Ichthyocentauri (Fish Centaurs).

Chiron is a Centaur.

Korybantes and Picus (which may be the Ichthyocentauri) are also called the sons of Cronus.

According to ancient texts (via Theoi.com) Apollo has at least 50 children

ASKLEPIOS

KORYBANTES SAMOTHRAKIOI

ION

KORONOS

ZEUXIPPOS

APIS

LINOS

PYTHAEUS

IDMON

AMPHIARAUS

EPIDAUROS

HILAEIRA

PHOIBE

IAMOS

ONKIOS

ERYMANTHOS

AGREUS

ELEUTHER

KHAIRON

TROPHONIOS

DELPHOS/DELPHUS

LYKORAS

PHILAMMON

POLYPOITES

LAODOKOS

DOROS

DRYOPS

AMPHISSOS

PHAGROS

LAPITHES

KENTAUROS

MELANEUS

ORPHEUS

LYKOMEDES

PARTHENOS

ANIOS

KEOS

PHYLAKIDES

PHILANDEROS

TENES

ILEUS

TROILOS

MILETOS

BRANKHOS

MOPSOS

SYROS

AMPHITHEMIS

ILIUS

AGREUS

LYCOREUS