Hi Kriston,

I really enjoyed Isaac Asmimov's nonfiction writings on science when I was 7-12 years of age. I'd poke around on wikipedia to get the book list then go to amazon and look up the titles. He has a lot of math in all of the books.

Almost all of this stuff is available at our local used book stores for $1-2$.

The complete set of his non fiction stuff would be a very good basis for any kid ( or adult) to learn about the world.

To answer your question, I really liked this book so far as a readable and technical discusion of numbers and their use over time.

http://www.amazon.com/Universal-History-Numbers-Prehistory-Invention/dp/0471375683