Actually, I had the same question. I have kill switches on video games and computers (with a dab of crazy glue to seal up the manual button) and I want to give my kids access to the lights, etc, but not the kill switches.
It’s not currently possible with the ST app. There has been talk that this will be added when they roll out hub 2.0. In the mean time, you can install this smart app and create an instance with only those devices you want them to have access to. Instead of using the ST app, they’ll go to the specified URL and be able to control those devices from the web