Start at the very beginning by using the proper words when giving them names for their body parts. There is no difference between nose, elbow, or penis and vagina when learning about their little bodies. If you start off with "wee-wee" or even worse "no no parts", you prevent giving your children the correct terms for their bodies, and if something ever were to happen, they would not be able to explain it to others as well.
During potty training, and when normal self-exploration starts, it's up to the parent to remain neutral and calm, not over reacting or worse yet, reacting negatively. Explain what the child is feeling, and where it is appropriate for them to do that (bedroom usually), and begin NOW telling them who can and cannot see or touch their bodies, and why. Also encourage them to give this respect to those around them by not touching others without consent.
All during childhood, be willing to discuss pee, poop, body parts, consent, feelings, hormones, menstruation and of course, sexual intercourse and the results. These topics are not taboo! Knowledge is power and results in children who not only trust YOU as a good source of information, somebody trustworthy and NON judgmental they can rely on.
Finally, please do not shy away from discussing SAFE sexual practices, and providing teens with access to condoms and contraceptives without judgment or questions. These things do NOT encourage them to go out and have sex - quite the opposite in fact, they feel empowered by knowing, less pressured to give in to urges, and hopefully secure enough to control their behavior in the face of overwhelming primitive urges. If they DO falter, please continue to be supportive or you might find yourself with an angry child who wants nothing to do with you.