Did Hephaestus have any children?

Yes; the names of his children are Eucleia, Euthenia, Eupheme, Philophrosyne; The Palici; The Cabeiri; Erichthonius, Periphetes, Ardalus, Cercyon (possibly), Olenus, Palaemonius (a Argonaut), Philottus, Pylius and Spinter.