JANE: What to do when it is that time in your girl child's life: 1. Sit down calmly and explain sex to her? 2. Buy her a book, video, or CD that gives her the details? 3. Buy her condoms and put her on the pill? Or do as many mothers before you did--just stick your head in the sand and hope she joins a convent. Of course these days your child may know more about sex than you did at her age, what with in-school health lessons, and out-of-school R-rated movies easily accessed on the TV, not to mention the Starr Report! In the days of fairy tales, sex was dangerous because so many women died in childbirth. Today sex is again dangerous because of diseases like AIDS. So what do we say?