When I was in elementary school, we often lived close enough to the school for me to be able to walk. Situations like these naturally lead to the concern of parents about children talking to strangers. Unfortunately, this fear has been all too substantiated by the stories you see in the news of people preying on children.
It might be some times, however, when you legitimately need someone else to come pick up the kids. In order to get around this safely, my parents came up with a family codeword.
If someone came to pick us up or wanted us to go somewhere with them, we simply asked them with a codeword was. If he could not supply it, we knew that my parents did not send them. Though we rarely had to use it, this gave my parents peace of mind.
When you’re coming up with a codeword, make sure that it is, on the one hand easy enough for the children to remember, but on the other hand not so easy that it could be easily guessed. We always had a word that was a name instead of the common object.