My 9 year old nephew loves to fish. So I bought a fishing panel and just bordered it a number of times, so that it is about 70 inches square. I haven't quilted it yet, but he loves it, and it's grown up enough that he can love it forever. How do I know he loves it? He wrapped himself in it and twirled around the room in it for a few minutes!
Cars are a good choice, too!