Why is everyone saying Edward and Bella have a kid?

From what I've read( which is pretty much everything you can read) vampires can't have children. I mean isn't that why Rosalie is so upset about being a vampire? She wants to start a family but can't because the are technically not even alive. I don't see how you can they will have a kid but I guess we'll see on Saturday. But I do agree with the Jacob will imprint on someone thing. There is a very good possability. Well I'm sticking with the VAMPIRES CANNOT HAVE CHILDREN!!!!!! thing.