kids: Bitcoin is an in-game currency where the game is the real world. To acquire enough of it to get rich you have stay in your bedroom for a couple of weeks while you figure out how to make the app work, then you have to keep your computer running basically forever, but you won't mind this because you have plenty of time on your hands and you don't pay for the electricity anyway."

Without wishing to be facetious, I think it might be easier to get a child to explain Bitcoin to all the dumb adults. Kids are so accustomed to virtual currencies from the worlds they play in - Club Penguin, Warcraft, Moshi Monsters - that they probably won't be fazed by Bitcoin. Even the mining part is so game-like that the average ten year-old should have no problem grasping it.