As scary as it may be, parents need to talk to their kids about people who might want to hurt them. The best way to protect your children is to get them involved in their own protection:
Parents need to be aware of possible predators. Typical signs are: someone who seems too good to be true, who offers extensive help to your family, who knows too much about your kids or kids in general, especially if they don't have children of their own. You should know all adults who you allow to have contact with your child.
Talk to your kids about pedophiles as soon as they can understand what you mean. As early as 3-5 years old, when kids begin to interact with the world, they're subject to being victims.
Tell your child you love them no matter what. Remind them that they can tell you anything and you will still love them with all your heart.
Don't be afraid that you're scaring your kids, but don't ask them to deal with adult issues either. Speak to them in age-appropriate language and give them instructions about what to do. They will feel empowered by knowing how to protect themselves. Be careful sharing your own experiences if you were a victim of sexual molestation, for example. Providing too many details and rehashing the tragedy can create a sexually charged environment and be harmful for your children in the long run.
Kids need to know that they have the right to say no, yell, or ask for help. It may contradict what they know about respecting adults, but if they feel threatened, they have permission to make a scene, or to run away to a public place. And they need to know they won't get into trouble if they were wrong. Let them know that no one has the right to hurt them. Teach your child to call you if a stranger arrives when there are no other adults around.
Make sure your kids know what is acceptable behaviour, and what is out-of-bounds. Make sure they understand that there are private areas of their bodies that no one else should touch.
Rehearse your child's response to danger. If he/she doesn't practice it, your child won't really know what to do. Telling your child to yell for help isn't enough. In the face of danger, a child could forget, so rehearse, role-play, and practice what your child should do.
Remind your children that predators don't necessarily look scary or strange. A dangerous person could look like the person next door, or even be someone they know.