Have you tried more factual books for kids like sports or tornadoes or sharks, that kind of stuff? Have you tried taking him to the library and letting him explore and choose a few different types to try out? What else is competing for his attention during free time? If video games or tv are options, some kids will usually choose those. Does he have trouble reading? Sometimes if you are offering books that are too hard, it may feel like too much work. Just some thoughts.