Shortly after age 2, the Pop Up Space Facts and Pop Up Dinosaur Facts books from Barnes and Noble became winners here. They are pretty fragile but he still pulls them out about once a week close to a year later. Around 2.5 we were reading them repeatedly for hours daily. These books are meaty and I think targeted for 8 year olds but if you have a kid who loves the subject matter and pop up books, it is worth considering.