I'd go for variety - breadth instead of depth in specific areas like math). At that age, exposure to as many different topics as you can possibly provide is the

I'd go for variety - breadth instead of depth in specific areas like math). At that age, exposure to as many different topics as you can possibly provide is the secret sauce - it a long term investment like no other. I'd find the best rated books in all ten categories of the Dewey Decimal system. Some of them will open up an entirely new ways of perceiving things.