While it's important to allow our young children to discover the beauty, magic and wonder of this world, it's also crucial to teach them that dangers do exist-- especially when it comes to strangers.
Super important-- define "stranger" for them. Obviously, strangers are people your children don't know but be sure to explain there are "good" and "bad" strangers. Tell them "good strangers" like police officers, firefighters, security guards, and teachers at school can always help if they get lost or find themselves in trouble. "Bad strangers" may talk nice but may try to trick them or take them away.
To keep your kids safe make sure you know where they are at all times, that they know their name, address and your phone number, and that they have safe areas to play, safe streets to use, and safe places to run to if in trouble.
Most of all teach your children to be assertive and trust their instincts. Let them know it's okay to disobey and run away from adults they don't know when they feel uncomfortable-- especially if approached by a stranger in a vehicle.
For more information on how to protect your kids from Stranger Dangers go to : http://www.ncpc.org/topics/violent-crime-and-personal-safety/strangers