Do you know what movies your kids are watching? How about shows on TV? What books are they reading? What are they looking at online? What music are they listening to? Do you know the content of all of it? The answer to these questions is exactly why we need to have an open relationship with our kids. You may think that 8, 9, 10 years old is too young to know about topics related to sex, but I counter that they already know something. I'll use the Twilight example. I know that 9 and 10 year old girls have read this series (numerous times) and watched the movies. Have you read them? I have. And I would not want my daughter reading them when she gets to that age. These books have blatant aspects of lust and sex in them. If your daughters are reading them, have you talked with them about the books?
When I was a kid, my mom had 'talk time' with each of us at bedtime. 'Talk time' was just that, a time each night that was just her and me (or my brother). She started when we were very young, part of our bedtime routine. And we would just talk, about our day, about what was going on in the family, what we were thinking about, what was happening at school. Little did I know that she was making a way to talk to us about some of the sticky subjects of life. Talking with your kids about sex can't just be a one time thing. It has to be a topic that is open anytime. You need to decide where your ins are. Sometimes they are tie-ins: songs on the radio, a scene in a movie, a book. You can use these to get a sense of where your child is at. Ask what they think about what they heard and saw and then talk about it with them. Let your own opinions be known, not in a lecturing way, but in a nurturing way. Other times it is a subject that you just have to bring up. I was reading how they are finding some girls hitting puberty at a very young age (as early as 7). 7! I was shocked when I heard that number. So we need to start preparing our kids young for changes that will be happening to their bodies. I remember when I was in school we had the 'puberty talk' when we were in grade 5. I would have been 10. I also remember when my mom had the same talk with me, it was the year before when I was 9. I also remember how many of my classmates had only heard about puberty through Judy Blume books and Teen magazine until that point in time.
Chances are, if you haven't started talking to your kids about sex by this age, they already know something about it. What is that something? That depends on your kid. Usually, girls are a little more mature in this area (for the time being, some boys catch up pretty quick). Some of them know too much. I remember a classmate of mine showing me her brother's stash of X-rated magazines when we were about 8 and I was shocked. I was a lot more innocent than she was to say the least, but that had a lot to do with how my parents raised and protected me.
I wish I had a good book to recommend to you to help you along with this age group, but I don't. My kids aren't here yet and the kids I worked with on this topic were older than this age. I speak as a parent anticipating this topic with my kids and a teacher who has taught this age group. I did find a great list on Amazon that has the bestselling books on this topic for all ages, so the books range from pre-school age to teen:
The ones that stand out to me are "The Period Book", "How are you changing" and "Almost 12". But I haven't read any of them myself. They are ones that I would look into if my kids were at this age.