I must admit, the topic of sex is uncomfortable for me (or my husband) to explain to our children. Neither of us EVER had a sex talk with our parents. As a result, A.) We don't feel comfortable communicating anything about sex, B.) We don't know how to talk to our children about it.
My husband feels very convicted that it is vital for parents to introduce the topic first to children so they have a baseline, and can know when they hear something (which they will), they will trust us, and know that God's way is best.
My husband first learned about sex in Kindergarten (age 5) when a classmate stole a playboy from his older brother. While I was mortified when he suggested we talk to our six-year-old son about sex (I was then pregnant with our youngest). He was correct, it was an appropriate time to introduce some very basic facts about sex.
The first two books recommend you introduce the book as a regular story, such as at bedtime. --In my opinion, it is unrealistic for parents to believe they can have a single talk with a teenage child about sex, and then expect them to somehow navigate through a sexually-driven culture with very little help or guidance thereafter. If we want our children to honor God with their bodies, we must be real, and they must be taught. I can say that I was raised in the church my entire life, and entering into marriage, I had a very unhealthy attitude about sex.
Each parent/couple need to evaluate what the long-term goal/approach with this topic should be for their family. This book series, while initially shocking, has proven to work very well, effectively, and answer most of our children's questions. Keep in mind that the age levels are suggested, not concrete. For our sons, we have found the age guides appropriate; perhaps it is different for girls. If you happen to order a particular level and find it too informative, I'd suggest you read the level prior. Prayerfully consider your position and willingness to teach your child this subject.
This book has too much information in it for this age range. Our little girl is almost 11 and she didn't like reading the book so we put this book and book 4 away and will pull them out again in about 6 mo.
We have used the first 3 books in this series. My husband and I have read through them together with our 2 older sons (10 and 9) and they have loved it! We are introducing many of these subjects to them for the first time and we'd rather be the ones to do that than movies or their friends. They haven't been uncomfortable with the topics because we are all discussing together. We have read through the 2nd book with our 7 year old daughter. We plan to begin reading the fourth book when our boys are 11 and 12. We've been VERY pleased with the series.