Teach your kids to not divulge personal information such as: their family, any telephone numbers, their school's name and location, their home address and anything about themselves.
If your kids use chat-rooms make sure they understand that not everyone may be who they say they are. For example an individual who says "she" is a 15-year-old girl from the state of California may really be a 44-year-old man in a different state or part of the world for that matter.
Always monitor your kids Internet activities and leave nothing to chance, this is just plain common sense parenting that should be taken seriously. Online child predators exist and are always in search of an easy target. Follow the above advice to prevent your kids from becoming that easy target.