Teach them how to make collect calls from a pay phone. Keep all emergency numbers within view of your phone. Teach your children how to call 911. A child should never answer the door without an adult present. When answering the phone they should not give out personal information and never tell a caller they are alone.
Nothing is better than parental supervision.
Your children should receive permission and never go anywhere alone. Encourage your children to use the Buddy System, two or more children when playing or walking to and from school. Warn your children not to talk to strangers. Explain what a stranger is. Your children should never answer questions, give directions, accept gifts or help an unfamiliar person find anything.