Needs I would definitely be giving that level of supervision and more. No bedroom door, if they go to a friend's house, I want the parents contact details, will speak to the parent every single time my child goes there and regarding school- I would have no issue with being completely open with the staff, tell them what had happened, and expect them to facilitate my wishes while my daughter was in school. The time during the school day that she is expected to be there, they have a legal responsibility toward her well being and safety. Would they want child sex offences and rape cases in school? I think not. In fact, they would probably have deep concerns if it had happened at home and I am sure would help a parent follow the correct avenues and contact the right professionals to putting a complete stop to such behaviour.
And yes, maybe the 12yo would unjustly feel emotionally abused, but my own daughter could call childline if she wished. I would hope that our relationship is one where she will listen and know that I am doing what is in her best interests 'My mum is trying to stop me having sex and won't let me be alone, I am 12 years old' How will that sound to herself when she 30?
I think it is the long run that needs addressing here, what happens if a parent allows and facilitates the sexual nature of the childs relationship?
Child grows up with little to no respect for herself, possibly ends up pregnant. Pregnancy terminated would mean that the child has to grow into adulthood with the guilt. Pregnancy kept would mean a very poor continuation of childhood, propelling into responsibility way too fast, lack of social development, affected education etc. How would the child reflect on adult intimate relationships? Is it all about sex? Is she worth more than her body? Is there nothing more to life? Would she feel dirty, used, damaged, be able to mature on to a level where her and a partner could have a truly open hearted relationship without feeling disgusted with herself? How on Earth would the growing child feel about the people who were supposed to look after her, educate and protect her? And what if she ever came across a thread like this? I would say that this is enough emotional distress and definitely a hell of a lot more as damaging as an over controlling parent!
If the child does grow up for the next few years under a watchful eye of parents, they may feel that they are being treated like a child and feel anger, resentment and perhaps hate towards their parents. At a more sensible age (and hopefully much more educated) they can continue as they so wish. But the likelihood is that the child develops into a woman who understands a bit more about life and love, and may look back at what their parents did, and actually thank them for being good parents not out loud though, no teenager does that I would rather preserve my childrens' childhoods, knowing that even if they hated me for the rest of their lives, I did the right thing.