As much as it might be a grand idea, it won't be possible. I was in the unenviable spot of having to keep a very close watch on one of my kids activities for safety reasons, they will find a way to meet up with people unless it's an outright whitelist only, and in that case they just go to some public wifi to go around it. There are plenty of sites out there that people are not commonly aware of that get used and traded in person that anyone trying to do basic category filters is already lost to.