Wow, thanks for all the great ideas! I am pleasantly surprised at how many responses my slightly vague question generated. John and Mitch, I agree about kids laying on the button, which is why I would do a logical AND between the button and the insulated track (which I realize still isn't foolproof if the train is parked on the insulated track AND the kid lays on the button). Maybe I'll add a thermal switch for good measure.
I hadn't thought of delay relays, and for this little starter layout I don't think I want to make things more complicated then they need to be, but it's a neat idea. I did find this nifty jack-of-all-trades relay that I might try if I had one laying around: https://www.amazon.com/GAEYAEL...-240V/dp/B07CH84BF6/