I read somewhere that it's a 50/50 chance for vampires, too (although I don't remember where). However, I have yet to get a normal child from a vampire/normal couple.
That is what Pam and I were talking about the other day. I believe, one couple out of five that had mixed parents have a normal child, other than that, they are all vampire children. Oh well, I love the eyes on the little ones, they are adorable.