Do see this video that teaches a child about bad touches.
"My Body Belongs To Me" - http://www.youtube.com/watch?v=a-5mdt9YN6I&feature=youtube_gdata_player
It isnt just kids who need to know but also parents who might be living in self denial that such things occur far more commonly and are not just statistics in the newspaper. Its also a lesson to the casual adult who might unintentionally invade the privacy of a child. Yes. We have to start treating children like little persons who have rights too. For instance knocking before entering closed doors. And above all the video emphasises the importance for parents to believe the child rather than hush up or scold.
Its important to teach "dont talk to strangers or take gifts from them". But its important to know that the major damage is done by known friends. One, the child is likely to lower the guard against a known person and secondly, is less likely to complain against a close relation or friend of a parent.
Its very important that children are also taught to respect other peoples privacy so our children grow up into conscientious adults who respect others' bodies and also stand up against crimes.
Most importantly, try and keep the communication line open between your child and you for as long as you can. Answer all questions with sincereity incuding those about private parts right from childhood and hopefully they will turn to you in their teens, when most kids start claming up. Remember, what your child tells you and how much they reveal will depend on what kind of reactions they get and grow to expect. If you are going to freak out, they will learn to shut up or turn to someone else.