I don't know what kids are interested in either.
My thought would be a game of some sort. I've read a number of posts from what appear to be young folks trying to creates some simple game.
Perhaps "Wack a Mole" might be fun and allow venting of excess testosterone. The Mole could be an LED and the wack some robust button. In the advanced Wach a mole you could add a small RD servo and have a physical "mole" pop up.