It's fiction. The art involved is quite impressive without being dressed up in a silly story about the secret children of Jesus. If I wanted that, I'd re-read Preacher by Garth Ennis. That has vampires, alcoholic Texans with God-like powers, and Arseface. Albino assassins just don't cut it.
I'd like to see a The League of Extraordinary Gentlemen style movie about Leonardo Da Vinci, perhaps fighting crime with his futuristic inventions. Of course, the real Da Vinci was supposed to have been more interested in coming up with designs than building them. But maybe that was the Clark Kent version of Da Vinci, maybe he had a secret ally implementing his designs while he played the mad professor.
That's eminently more plausible than the claim that anyone would keep it secret if Jesus had children. They'd have trumpeted that from rooftops.