What's Your Angle, Pythagoras? A Math Adventure by Julie Ellis
Another really nice recently published math picture book. This would be more like ages at least 6 to 10 I'd say. The math, concepts and vocabulary is higher level than other picture books. If a child is content to have concepts go over his/her head, you can read aloud to younger kids just for the story value.
This math reader is written from the standpoint that Pythagoras is a boy: "Long ago in ancient Greece, there lived a curious boy names Pythagoras. Pythagoras just couldn't help poking his nose into places. Sometimes, his curiousity got him in trouble, but sometimes it paid off."
It goes on to tell in a story ways he thought through problems that perplexed adults, how he found the formula for the Pythagorean Theorem based on rope-stretching and finding the famous 3, 4, 5 ratio, how he discovers square numbers, and how that knowledge was applied to distance problems, all in a story context with attractive illustrations. Really nice picture book to add to math / science history studies.