My cousin's four year old son is obsessed with things like quarks and infinity. He insists to his mother that infinity is the last number. She isn't so sure, and wants to know more about things like strangeness. I don't want to determine this kid's future, but it seems fun to feed his curiosity. And since my wife's babysitter was Murray Gell-Mann, the responsibility has fallen partially on my shoulders to help answer his questions. What kinds of information can you recommend that I give to his mother so that she, an attorney and not a mathematician, and her son can learn more about this information. In particular, what kinds of books, games, and projects would introduce him to other neat ideas in mathematics and physics?
I'm looking for science fiction/speculative fiction without depictions of sexual violence. What books should I read?