There are a bunch of people doing really good and interesting work with math and kids these days. Sasha Fradkin is one of these. She has a gift for tapping deep into kids’ mathematical minds and for writing about the beautiful ideas she finds there.
She has written a book—Funville Adventures—that is definitely worth your time and money, and she’s funding its publication on Kickstarter. I have pledged. You should too. I promise you’ll be glad you did.