It is most certainly the case that what is good for children is often a matter of opinion. Some parents think nudity is a definite evil and keep their children from it. Other parents think knowledge of sexual matters is natural, that nudity is healthy so that their children grow up knowing and respecting the human body. The latter believe that frankness and openness are better than prudery and misinformation, and I agree. In school terms some people think that learning a foreign language cements the knowledge of one's native tongue and makes for a wider awareness, a more flexible attitude, and better international relations.
Teen years are times when hormones kick in, and experimentation and curiosity replace blind trust.
Plato's definition is naive at best, suicidal when applied to an educational system. This definition was central to the educational philosophy of Millard Scherich of Oklahoma State University. You know it does not. F.C.S. Schiller says the function of truth is to lead us to new truth, not to be hoarded, saved, encapsulated. Every person with any education realizes how much more knowledge is still out there to be learned.