So much can be discussed even in a secular discussion, but even then it will be tangential. Groups that make no effective endeavor to bring converts in, and especially to convert spouses of their own members, will of necessity become smaller and smaller. But that is tangential to what public schools would bother with in speaking of marriage among members of different Faiths or no Faith. As for parents, they seem to be either too mixed up, too distant from their children, or just too ignorant to educate them in ways they may subscribe to. All of this is fodder for discussion.
Sex comes in in another way in the information age.
The access to information on the Internet that is readily available to many children includes access to pornography. But given the way groups of children isolate others and the way signs of social estrangement get ignored by parents and teachers, many children are so lonely and frustrated that they will do anything to get any loyal friend who is compatible with their make-up. But the parameter of sex cannot, certainly among neoadolescents and adolescents and new-marrieds, be left in the realm of tabooed discussions. When things go this far, it is clear that society has become dangerously screwed up and has run into a dead end. On TV recently, the case of a boy knowingly brought up as a girl because of an accidental lose of his male genitals, shows how willing some doctors are to experiment on real humans and so stupid and unfeeling as not to monitor the results intelligently and honestly enough to acknowledge that their pet theory is wrong.