Is a fantastic book for a kid who is very interested in math, but not yet reading. Basically it depicts the prime factors of the numbers 1 to 100 with very clever pictures. It was the favorite book of my son when he was about 4.5, and we still call prime factors monsters internally (eg, reducing fractions involves "monster battles" and so forth).

http://www.amazon.com/Count-Monsters-Richard-Evan-Schwartz/dp/1568815786