Dave Winer has some good advice:

I’m often tempted to offer advice to the parents, but I won’t offer it unless asked, except this. If you have children, there’s a good chance one or more of them will not have children, and you should love them the same, and provide models of acceptance while they’re growing up, by bringing childless people into your home, so the kids know that this is one of the legitimate choices in life, offering proof that you won’t love them any less if they go down that path. And here’s the hard part, imho, for people with children – keep that promise.