Do you know James Stevenson?
Because if you don't, you should. Just go to the library this week and go to the S's in the picture book section and check out every Stevenson book your library has available. Stevenson is good for the very youngest up to middle school. There is subtle humor is on every page, and yet, you don't need to understand the humor to enjoy the story. For example, whenever Grandpa is starring in a Stevenson story, and he is telling a story about himself as a young child, his young-child-self has a black mustache that matches his old-man-self's white mustache. Even though he's supposed to be around eight.
That was a terrible explanation; just check these books out for yourself and you'll see what I mean!