No one looks forward to having talks with their children about uncomfortable situations but no matter what your child's age there are talks that you should be having with them on a regular basis.
For younger children, it is important to introduce them early to the concept of good touch, bad touch. This allows them to have the words and the confidence to talk to you if they experience a bad touch. It is a horrible thing to think about but if someone does approach your child you want them to be prepared, to know that they can say no, and that they should come and talk to you about it. If you do not talk to them about it first, then you leave them open for manipulation by a perpetrator.
So how do you approach the subject? You can start by defining the terms "good touch" and "bad touch" for your child. "Good touches are touches that you like, touches that you feel comfortable with and that make you happy, like a hug from mommy. Bad touches are touches that make you uncomfortable or sad. They are touches you don't want. Sometimes people try to touch you in your private parts or ask you to touch their private body parts. These are bad touches."
You can then go on to discuss what parts of the body are private by saying, "Do you know what parts of your body are private? No one is allowed to touch you in a private area."
You can then ask them for examples of good touches and bad touches. You should also ask them if anyone has ever given them a bad touch. To end the discussion, review with your child what they can do if someone tries to touch them and who they can tell or turn to for help.
There is a wonderful resource that can be accessed by googling "Good Touch, Bad Touch, Secret Touch: Your Body Belongs To You"; the first link is a quick read and a great primer for parents about to have the conversation with their little one. The University of Iowa Children's Hospital also has a very useful webpage on Good Touch, Bad Touch with talking points and examples to go through with your child.
Children as young as 4 years old can begin to understand the concept of good touch, bad touch, but even younger children can understand that parts of their bodies are private. There are some non-threatening books to help introduce and illustrate the concept of private parts. One such book "Some Parts Are Not for Sharing" illustrates this point with a children's story about fish.
Like all tough talks it is not sufficient to have the talk once and then hope that your children will seek you out should they need to talk. The conversation needs to be repeated on a fairly regular basis to reinforce the topic and to make sure your children understand that it is not taboo to talk about their bodies or if they are ever uncomfortable.