As parents it is never too early to begin building the foundation for values, an important part of sex education. The big lesson comes in the 4th grade while the boys are still disliking the girls. By the 5th grade, my son bragged about girls liking him. Not that he was interested, he just couldn't help noticing how much they were liking him.
In these times, teaching sex education is easier for us than it was for our parents forty or so years ago. Today, we are surrounded by every possible example of what not to do. We don't have to work hard to point out the consequences of irresponsible sexual behavior. It's everywhere! Political leaders, religious leaders, local leaders, they are all hanging out their dirty laundry for all to see. Choose any hour of any day and you can find an example of what not to do with the opposite sex, or even the same sex for that matter, (grin).
If you handle it properly, sex can be made to seem so disgusting to your 4th grader that he or she should be able to get through their teenage years not wanting anything to do with it. If that isn't enough, we now have AIDS. Let's face it, our parents were not able to tell us that sex would kill us. Quite frankly, it should be easy to get the message out. The secret is starting early.
First, you set a good example of what responsible behavior looks like. (Make sure you are not the disgusting example they see every day.) Second, take the time every day to point out the consequences people around you are suffering due to their disgusting behavior and why. Thirdly, don't forget to point out that the first time they have premarital sex, it will probably kill them.