Those Uncle Albert books look great, ColinsMum--thank you!
shellymos, would your little guy be interested in biographies, I wonder? The Jeanne Bendick books about Galileo and Archimedes might be interesting in that case. We also tried Luetta Reimer's "Mathematicians are People, Too," but somehow didn't care greatly for the writing (which tends to be a bit of a dealbreaker around here, I'm afraid), and the content was a bit "lite" as well. Charles Seife's book about zero is the biography of a number, so to speak--that one was a lot of fun.
Edwin Abbott's "Flatland" might appeal to him?
Not stories, but fun, are the Martin Gardner collections of puzzles of various sorts; maybe he'd enjoy "Gotcha," which is his paradox collection?
Harpo's favourite math book right now is Starbird and Burger's "Heart of Mathematics." It's a textbook, but written in a very engaging conversational tone (and hey, it comes with 3D glasses!!). Might be fun? (It's ridiculously expensive new, but there are scads of cheap copies on abebooks--we got a brand-new copy of the previous edition for literally pennies plus shipping.)
Hope that helps....
peace
minnie
