Actually, the best time is anytime you feel you should start showing responsibility in what they learn, and when they learn it. As you teach your child, from newborn to teenager, you need to incorporate the rights and wrongs in all things, including sex. Do not be shy about it. Be forthwith and forward. A child is most acceptable of new and free thoughts prior to the age of 12. So, if you cannot talk about it, play a tape while they sleep. Imprint upon their young minds, that sex is NOT recreational, and that bad things can happen to those who are loose with their bodies. Of course, don't forget to mention drugs, alcohol, gangs, peer pressure, etc. Just take time and teach your child. Get to know them, and let them know you. Conversation and communication are key factors here, and the most important next to unending love, and respect.