A: First, download my sex ed handbook, and use it as a guide. It has diagrams; it has information and will give you tools to use with her. Ideally, you would have talked about sex before now because, at 13, she is probably already going through puberty.
At 9 and 10 you should be talking to children about what to expect with adolescence physically—with menstruation, breast growth, hair growth, acne, sexual thoughts and ideas. At this age you also need to talk about the mechanics of how a baby is made. You need to talk about ovulation and what happens when a woman ovulates, and you talk about how sperm is produced as boys move into adolescence and adulthood. Then, you talk about intercourse and what it is. This is when you can start planting the seeds about your moral values and what you want for your child sexually.
You also don't want to forget to talk to them about how normal it is for them to check out their own genitals, to touch them and see what feels good. Make it totally normal for them to touch themselves and to start exploring what will later become masturbation. You want them to feel comfortable with their bodies.
— Dr. Laura Berman