Since you're going to use Alice anyways, I figure I'll steal from the book on this one and suggest having the kids do something they can interact with. In one exercise, I recall making a room filled with several pieces of furniture, and I had to make them move during the program by setting an event to 'let mouse move objects'.
I think something similar (or same, if you want to do that
) would be a great experience for kids that age who are looking into programming as a possible future career.
That's just my suggestion. I'm sure several other people will have some ideas, too.