My initial response, once again, is that this subject is best discussed between a married couple and their spiritual father, not on an Internet discussion forum.
Their spiritual father? I don't think any couple would go to their spiritual father regarding sex...
Besides, whatever their father says (for eg. sex should be used for expressing love as a tool for marriage instead of for self-pleasure), why can't it be the view of the entire church. I mean, different fathers could say different things.
Btw, the parents should remember God created sex, so I don't see how they would view such talk on a religious board to be "bordering on the pornographic." And I just don't think it's healthy for a child to be ignorant about sex in general until they reach "the age of adulthood."
Also, what if certain positions are considered a sin, but they're ignorant of this?