Our club here in the Atlanta area sets up a kids layout at various shows throughout the year. The layout has four tracks / trains in operation with four CW 80 transformers, one on each corner.
We tried different methods to limit the maximum amount of power each transformer could send to the track and the best was to install a small potentiometer on the back of each transformer. This allows us to adjust the maximum power level very easily. We've used this method for about three years now and surprisingly, the kids still haven't figured it out.