"THE talk" for me became "THE talk" when dd turned 10 and still hadn't asked HOW the mom's egg and dad's sperm gets mixed up. We'd talked about everything BUT sexuality between two people, and I realized, "Crap. I have to bring this up without following her lead." The kids even have the basic idea of genetics, but never asked about sex. Even when I used the word in conversations about why some children have children (teen pregnancies).
Reading Diapers to Dating was really helpful to me. I realized what made "THE talk" into "THE talk" instead of just "A talk" was that I was giving what seemed to me like momentous information (how intercourse happens, that people have oral sex, and wanting to touch lightly on STDs, rape, birth control, intimacy, and choices) was that I was no longer answering questions, but starting the conversation. And I articulated to myself that there would be many such talks, I just had to jump the hurdle of this one.
So I asked her one night if she knew how the dad's sperm gets to the mom's egg. She didn't. I told her the dad puts his penis inside the mom's vagina, and that the sperm came out the same hole where he pees. She looked a little skeeved. I said "I know it might sound weird, but people do it."
Then I told her I wanted to talk to her about sex, and I thought it was important because some kids think it's a good idea to have sex when they're even as young as she is, and I wanted her to know why it's not a good idea at her age. Told her some of the things 12yo boys had said to me to talk me into it ("If we only do it for 5 minutes .... ") and told her I was glad I knew they were wrong so I didn't make a bad choice. Talked about how some boys and girls think that if you love each other, it means you should have sex, or vice versa. Talked about what to do (again) if someone tries to touch you in a way you don't like, and explained sometimes people your age or grownups or even your friends or family can try to make you do things you don't want to do. (I was sexually abused by a family member and later experienced attempted rape, and was too ashamed to ask for help, so this is an important topic for me.) We talked about her 12yo stepsister's friend who was pregnant, talked about abortion, adoption, teen pregnancy.
The whole conversation lasted less than 10 minutes, I think. Once I got past starting the conversation and telling her *what* sex is, the rest went easily, and I didn't feel pressured. I ended things by asking of she had any questions, and told her we'd talk more about it as she got older, and that it was important to talk about. Gave her suggestions of who she could ask questions of if she had a question and didn't feel like asking me about it.
I really did expect that they'd ask. None of my kids (10, almost 8, almost 6) have ever asked me how the sperm gets in -- they get their early explanation (like when they're 2ish) without details, ask a few questions as they get older, we address masturbation, menstruation, anatomy, genetics ... but sex just never comes up.