My DS6 does this. We have implemented a system in which we write down his big questions so that mom has time to research the question and give it the time it deserves. This has helped alot.
That's a really good idea, I should do that. My DS6 often comes up with these questions (factual ones I can't answer, I mean) on the bus, and I say "I don't know, but we can look it up when we get home" and then neither of us remembers. It's almost enough to make me try mobile broadband... The "meaning of life" type questions haven't so far been a problem, as he hasn't been upset about them, just interested in talking about them, so we just do. I did get to answer "so how do people catch HIV mummy?" in a restaurant toilet a few months ago, which was interesting!
