Not the teenager's phone. The parents paid for it... and continue to pay for it through the subscription of cellular service. Unfortunately any attempt to keep the parent out would be accurately described as theft or destruction of property.
No. Android doesn't. Google does. But not everyone wants to have anything to do with Google. Some OEMs do, like Samsung. But it's not in AOSP or basic Android feature. But my point wasn't to spy on the kid. It was device ownership.
Edit: Even this gets downvoted. You guys are fucking lunatics. A Child... using a phone given to them, can't even consent to the shit Google does to you legally. But you want their data "protected" from their parents so that a parent can't at least enforce decent digital hygiene. Ya'll fucking dumb. Your kids are going to do dumb shit and you want the parents who are supposed to be responsible for raising the kid to have no power to actually raise them even though it's literally the parents device.
Well, by that logic the parents can do whatever they want with the phone, yes, including stopping cellular service or resetting it entirely. But the OS would still protect the teenager's data from unauthorized access.