Some accessories operate off of buttons and should provide entertainment for your kid - 352 Icing Station, 128 Newsstand, 445 Switchman, 145 Gateman. I use them on my portable layout for shows and kids like them. Does Gargraves make conversion connectors for tubular track? If so you can insert an operating track section for operating cars that use them such as the 3461 dump car.
If you can't find #90 controllers, Trainz carries some K-Line pushbutton controllers that mount on the surface of the layout.
