The only complaint is that the teeth on the gears are too small. The gear on the shutter wheel and the perpendicular gear on the shaft driving it tend to disconnect way too easily. Thus if an unsteady hand is running the crank (as 8-9 year olds tend to be), the motion effect is not as pronounced. Perhaps redesigning the connection as a worm gear or at least making the teeth on the gears larger would solve the problem.