Marty, Re: "The Kill Everything" button on the iCab app requires you push and hold it for 3 seconds before it will HALT. "
My observation of kids using apps at shows is that some will lean on a button icon until they observe some visible/audible action (or their attention span expires). Three seconds of pressing is very common. We exceed 3 seconds pressing on the quilling whistle. Kids will experiment with every button on a screen, and it's fun (for them) to do something that causes the show operators to come over and restart the train.
The best app for letting the kids experiment is the LionChief Bluetooth app. Kids learn it quickly and always seem walk up the iPad and get the train going on their own. The control icons are recognizable to novice users. Just enough to run the train. I occasionally have to come over to reconnect the engine. (But why they choose to run the train in reverse more than half the time after exercising the reverse icon remains a mystery).
Contrast the LionChief app to the complexity of the iCab app (which mimics the Cab2) where half the icons require operator training to recognize the icon and understand how it works. We can use a 101-level app in addition to the full capability app.