That may be changing.
I kept looking for simple books about government, elementary level but that goes further than merely that we have three branches. I found one at the library that I like finally. It's called How the U.S. Government Works by Syl Sobel, it's a Barron's book. It's simple but gives enough information for the start I wanted him to have. All went as usual until we got to the Judicial branch, then things got going! Suddenly his eyes were wide open, he had comments and questions, even opinions! AND THEN...there's more! I also brought home a video documentary called Understanding Government - The Judicial Branch. I was watching it while he was doing something else, he started heading upstairs but stopped. I can hardly believe what he said, "Mom, that's interesting, turn it off so I can go upstairs!"
A couple of weeks ago, I brought home the video from the same series called The Executive Branch, but he was totally uninterested; this time we've got a winner. Perhaps I should have expected this, he loves to watch Matlock.