"If I'm the father of two children and one of them is a boy...

"If I'm the father of two children and one of them is a boy what's the probability that both my children are male?"

At the risk of upsetting Robbo who actually want's to talk about First Australian Resources, I've thought about it some more, and I think the correct answer is actually zero. Semantically, 'one' without qualifiers means exactly one, so therefore having both male would be impossible. However, should the wording of the question change to "at least one of them" I am leaning to agreeing with Vege - 33%, but still not quite convinced.