Another thing I came up with as a kid, but no capital to put it to play was a free energy device. You have a light bulb powering a solar panel. You need to initially feed it with the same energy required for the light bulb for a small instant then it powers itself, and you can tie into it to get as much energy as you want. Of course, this would not actually work but as a kid I thought it would.
Another thing was you have a disc that can rotate, and you have magnets on it at an angle, and more magnets on the stationary part that are spaced in a way where the magnets never fully align, so the force of one would push the wheel one step, then next magnet would push it again and so on. It would turn forever. Not that it would work though but as a kid I thought it would. In concept it seems that it could work though but or course you can't have perpetual motion.