When your nephew gets more fun out of the hammer than the actual toy, it's probably not going that terribly well. These helmet/balls things sit on top and when they are hit/pushed, they fall down into the car below, hitting a trigger which then pushes the car through and out the door.
It does work (most of the time) but the cars have to be pushed up right up against the back of the little garages in order for them to shoot out when you hit the top, otherwise nothing happens. I guess the doors should only be shut for storage and fun can still be had, just as more of a general car and garage set really.
NB: This review is no reflection on the supplier who I would wholeheartly(and have done) given five stars to. It was a decent price and arrived both quickly and free of charge.