How many sons did Hephaestus have?

Hephaestus originally had one biological son, who was Erichthonius. He was 'born' when Hephaestus tried to rape Athena. However she escaped him and his semen fell to the ground, and actually impregnated Gaia. Athena became to child's foster mother.

There are some myths that Hephaestus did have extra 'sons' but they themselves could be foster children Hephaestus took care of during his exile. And they were Palaimonius and the 'Kabeiroi' on the island of Samothrace - Possible a group of craftsmen, who too were slightly crippled like Hephaestus