When I was little my parents couldn't always pick me up from school or from friend's home so they'd send one of their friends from work to pick me up. Sometimes I didn't know the people, and being that "America's Most Wanted" was my favorite show at the time- I didn't feel too safe going in the same car with a stranger.
To ease that fear, my mother and I came up with a code. If she was going to send someone to pick me up she'd tell them to yell out the secret word so I'd know it was okay. Most of the codes were corny, but they were random and frequently changed.
My mom and I had an agreement, if the first words out of the person's mouth wasn't the secret word, I would not get in the car.
I think that it would be a good idea for anyone with children to come up with a secret word of phrase that only the parent and child knows. That way if any sicko tries to pick them up and say, "your father told me to pick you up," your child knows that something fishy is up and to run away.

Good tip Lanni.

An excellent tip. What a pity that it has to be necessary.

When my children were young I was only too aware of the dangers of paedophiles, also that children are quite likely to be abused by a person they know. I told my children that they were not even permitted to enter the car or house of a person they knew without consulting me first.