I found this on babycenter.com
What your preschooler knows — and needs to know
Two- and 3-year-olds don't know what a stranger is or who's safe and who's not. While you can begin to teach these little ones basic safety, they're not ready for conversations about how to deal with strangers.
By age 4, though, many preschoolers have heard about strangers and can start learning safety rules. But they're still too young to be left unsupervised in public because they don't have good judgment or impulse control.
As you begin talking about strangers, keep in mind that despite sensational media coverage, stranger abductions are extremely rare. According to the Center for Missing and Exploited Children, only 115 children in the United States per year are victims of kidnappings by a stranger. And preschoolers are the least likely age group to be targeted.
How to begin talking with your preschooler about strangers
Start with basic body safety. As a prelude to talks about strangers, discuss general safety with 2- and 3-year-olds. When you go out, ask them to stay close. Also, kids this age are not too young to learn the names of their genitals and that it's not okay for most people to touch them there.
Introduce the concept of strangers. Usually, kids are ready for this by 4. "The easiest way is to say, 'Do you know what a stranger is?'" says Sherryll Kraizer, executive director of Coalition for Children and author of The Safe Child Book. If your child has no idea, tell her a stranger is anybody she doesn't know. You can point out examples on a typical day — a man at the grocery store or a woman in the park. To avoid freaking your child out unnecessarily, emphasize that a stranger is not necessarily a good person or a bad person — just someone she doesn't know.
After talking to her preschooler about the risk of approaching an unfamiliar dog, one BabyCenter.com mom says, "I drew the parallel that a stranger might be nice or not, just like a dog you don't know."
Sandy, the mother of a 4- and a 9-year-old, used the DVD Stranger Safety (part of John Walsh's The Safe Side series), which explains the difference between people a child doesn't know at all, those she knows a little, and those who are safe. "We've talked to the kids about who their 'safe-side' adults are — mom, dad, grandparents, aunts — and we've quizzed them," she explains.
Go over do's and don'ts. Define some rules about how to deal with strangers. For example, Kraizer suggests giving an older preschooler a specific game plan to follow if you become separated: "If you lose Mommy in the grocery store, go to where we pay for things and tell them you're lost, tell them your name, and don't move from that spot until I come to get you." Tell an older preschooler that if she's approached by a stranger, she should go straight to the person who's taking care of her.
Point out adults that kids can trust. Besides Grandpa and Auntie, give a few examples of adults a child can go to for help. "I point out authority figures like mall security guards and teachers and tell my daughter that they can help her if she gets lost," says Kathy. Sandy adds, "We explained to my son how to identify store employees — by their vest or by their post at a cash register — if he gets lost."
Avoid scary statements. To drive the message home, you may be tempted to issue warnings like "A stranger might take you away from me!" or "I might never see you again!" But that will unnecessarily frighten your child. "The conversation needs to be not what you're afraid of but what empowers your child," says Kraizer.
Repeat. There's no need to overdo it. But because preschoolers learn through repetition, you should underscore the message when an opportunity arises, such as at Halloween, during a vacation to Disneyland, or before a trip to the zoo, a kids' museum, an outdoor festival, or anywhere else where you'll be around crowds.