There are a lot of great DK books, Horrible Histories are fun, you could also try fictionalised stories based in history like The Silver Sword, I am David. You get the idea. My DD loved Ripley's and Guiness Book of Records. Weird facts but facts nonetheless! I actually learnt a lot about the world from fiction stories so it's not a bad thing. You could try stories from other cultures or set in foreign lands so that he is learning without knowing it.