I think it's the parents' responsibility first and foremost. Be honest, be open, and be accurate. Teach your kids what constitutes sex so they know if they are ever in a compromising situation or someone toes to pressure them into something and convinces them a certain behavior is not sex. I learned about sex when I was about 7. My mother, who worked as a nurse for many years, told me. She was mature and straightforward and pretty unflinching (dad was embarrassed). If I ever had questions later, she was willing to answer them, but I was usually the one embarrassed. I also learned in 6th, 7th, and 8th grade from different teachers, sometimes with the boys, sometimes separate from them. I plan on being very honest with my kids.