Little kids love spinning wheels. Generally I take the drive band off and just let them treadle. It's pretty satisfying even without the flyer whirring and yarn pulling in. They also like it when I tie some pre-made yarn to the bobbin and they pretend to be drafting and letting it feed onto the bobbin. (In that case, the drive band and brake are on so the whole thing is moving.)
Well, this is what happens when you give a 4-year-old some pink fiber, hook everything up, and let her spin. She loved it! And she was really proud of her yarn.