Scratch.mit.edu was made by MIT, the college, and is a game development program made for all ages, it is very simple, but has great potential, as you can make many more challenging things, take Griffpatch, a very talented scratcher, he has made very complex raycasters, online games, and even rigid body physics! Which Scratch doesn't have built in, you make the game from "scratch" so no add ons like rigid body, except they do have a site for that, its called scratchx!