Yes, I think we had similar discussions with our DS when he was that age. He was also fascinated by negative numbers and infinity, which sounds like a common theme on this board.
I have a very vivid remember having a conversation with my mother-in-law when DS was four, and she was adamant that kids could not understand abstract concepts until the age of 8 or 9. She had studied this in some childhood psychology class in college. I kept pointing out examples of very abstract concepts that DS understood: negative number, infinity, even the concept of zero, which the Romans never grasped (there is no Roman numeral for zero). She would not except it.
JB: DS8 had to go through allergy testing about a year ago... 72 shots in both arms. Needless to say he was not particularly happy, even with a large amount of numbing cream on each arm. It was the sight of the needle that bothered him, not the actual injection. DH kept him occupied by making him count all the prime numbers as high as he could go. That was a life-saver for getting through that ordeal.
Math is a great way to distract or calm a kid down!
Dazey: I had heard of the book, The Cat in Numberland, through this message board. It is a great suggestion. DS just read in and liked it a lot. Are there any other books by this author? Or other math books that people can suggest?