[peakok]

Basically you're right, and Paul is right too. This is just a matter of convention, it depends on what you want to hear in the question. If Jeff said "one of the children is a girl", but added "but we don't know wich one of the two is", this post would have never existed and we wouldn't have argued so much over nothing.

In the world of mathematical conventions you learn in school, the question is understood and you're right. In the "normal" world where you can quibble with language because there is no specific agreement, Paul is right and the question should be more precise. In both cases the conclusion remains the same : what a waste of time.