Vaughn doesn’t want children, but he doesn’t not want children, if that makes sense. Like, it’s not something he’s actively opposed to; he’s just not interested.
So if Desi were to say he wanted children in this hypothetical scenario (which you’re right would never happen!), Vaughn would be fine with that. He just wouldn’t spend any time with the kids, or allow the kids to prevent Desi from being available to him whenever he wanted. As long as it didn’t inconvenience him, he wouldn’t care.
That’s actually a good barometer for how far Vaughn would go in fulfilling Desi’s requests - as long as it’s feasible, and the benefit to Vaughn outweighs the inconvenience, there’s not much Vaughn wouldn’t do if Desi asked.