When I won't let my seven year old watch something on television I don't wait for her to ask why, I explain that somethings should remain private and that people do lots of things that are wrong for money. And that watching such things makes us part of the wrong.
That she can understand, that people act with bad motives and that she'll see many examples of it.
But most importantly I teach her by how I react to the vulgar and crass displays of sexuality.
And she also sees how her parents treat each other. Thereby we teach her what the relationship in marriage should be without having to say a word.
For certain children will be taught, the only question is by whom and what.
Excellent post!