If this is a concept that you can't grasp, then words will never convey it. It's simply a detachment from reality to think people are viewing their phones as a loaded gun and their child as someone hellbent on betraying them and causing massive societal damage.
The phone is the YouTube device. If they get a notification that their kid ordered from Amazon, they'll cancel the order and tell their kid not to do it again. It's seriously that simple. Just go and talk to a parent. They'll think viewing their phones as a WMD is insane.
Okay, so trust them not to access age-gated sites using your credentials then.