I think the kids (and adults) will get a much larger charge of actually using the transformer controls to run the train and modulate the speed, etc. Have ing a push button to run a canned sequence gets pretty boring very quickly. You're also creating a lot more work wiring horn and bell buttons for twelve tracks!
IMO, the KISS principle is in play here, a couple of hidden variacs to limit the maximum voltage, and the controls on the transformers function as designed, job done.
I kind of figured that pushbuttons would also have the added advantage of being easier and less expensive to replace from overly rambunctious use that kids (or even adults) could bring into the equation with the controls. It's a little more costly to replace transformers that end up getting their handles broken.