The Boy Who Loved Math: The Improbable Life of Paul Erdos
Bedtime Math: A Fun Excuse to Stay Up Late
We also started this book recently, and he has really enjoyed it so far:
Women in Science: 50 Fearless Pioneers Who Changed the World
It's amazing to see the influence Paul Erdős had on people. There is a children's story (that I read to my kids) about his incredible life. http://www.amazon.com/The-Boy-Who-Loved-Math/dp/1596433078
My son is 3 1/2, and he loves this book. He loves that there was a kid who loved numbers so much he spent his whole life studying them. He loves that he gets to see a boy grow into an adult, who grows into an old man. If you want to share your love of math with a kid, Erdös' story is a great one to share. It's also a great conversation starter about how much or how little to focus on any one thing. I love knowing Erdös' story, but I'm not sure I'd like to be him.
 - http://www.amazon.com/The-Boy-Who-Loved-Math/dp/1596433078/r...
I recently looked for some kids' books that would focus on the more interesting problems in math, rather than just counting. I was happy to find a few books that have helped him see math as more than just counting. My favorite so far is The Boy Who Loved Math: The Improbable Life of Paul Erdos.  I knew of Erdos, but I didn't know much about him. I learned from reading this book, and my kid loves it as well. He is fascinated with aging, and he now sees it as normal that someone would spend their whole life focusing on numbers.
We are also starting to enjoy Bedtime Math: A Fun Excuse to Stay Up Late.  The idea is to give your kid some interesting math problems to think about at bedtime. We've found that it's a good way to help him think about things other than the dark, and strange noises while he's falling asleep.
It's fascinating to watch this development. A few nights ago: "Did you know that one of the oldest questions people have asked is, How many stars are there in the sky?"
"No, I didn't know that!"
"How many stars do you think there are in the sky?"
 - http://www.amazon.com/The-Boy-Who-Loved-Math/dp/1596433078
 - http://www.amazon.com/gp/product/1250035856
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