I've heard many parents, on several occasions, make statements to the effect that they believe it to be harmful to discuss sexuality openly and directly with young children (I'm talking about kids aged 5-10 or so). Movies and TV shows with sex scenes (not pornographic ones, but unmistakeably nonetheless) are given higher age ratings, and many parents are careful not to let their children watch movies that feature sexuality or nudity, even in non-extreme situations. Many parents are upset at the idea of sex ed in schools, particularly for children under the age of 13-14 or so.
In all, there seems to be a consensus (not universal, but widespread in North America at least) that exposing children to sexuality is somehow harmful.
Is there any data to back up or refute that consensus? Any studies on links between exposure to sexuality (at school, through discussions with family, through the media, etc.), and, say, STD rates, teen pregnancy rates, depression rates, sexual abuse rates (as victims or as perpetrators), etc.? Note that I'm not much interested in "starts having sex at an earlier age" (the only effect I've ever seen claimed by a study), unless it is necessarily accompanied by abuse and/or poor use of protection.
I'm particularly interested in the effect of discussing the topic with children, i.e. the child who gets everything explained to them when they're 5 and whose parents are not shy about talking about sexuality in everyday life, versus the child whose parents hold off on "the talk" until they are 14 and try to never mention sexuality in the presence of their children.