Showing them the permissions requested, training them to not install things from outside the store unless they know what they're doing, explicitly needing to manually enable installation of software from the outside, etc etc.
That's it. You've done your job.
And if, despite all that, some people still want to continue to use their phones in a dangerous manner LET THEM suffer the consequences of their ignorance. Let them bruise their knee. They're grown ups, presumably. Some people just need to learn the hard way, and we shouldn't architect the entire system to protect that lowest common denominator.
You absolutely do not need to childproof the entire phone to protect people from themselves. For me, that's why it's patently obvious that this move has an ulterior motive.