My pickup form has the parents list the names and phone numbers of anyone they want to authorize to pick up and I encourage them to list a relative or close friend for times when they might be unable to do the pickup. The page is worded such that I can release the child to anyone on that list. At the same time I would never do it without a call. If someone from the list showed up I would be callling one of the parents before agreeing to release depending on the story the person gave me. I would find it odd that the parent could call the contact and not call me. I have had it the other way around where a parent calls and says they are still in a meeting or got a flat tire and going to be very late and have asked me to call the person on the conact list and see if they could pick up instead.

I agree that abductions by known people is a possibility. At the same time in the grand scheme of parents with flat tires or medical emergencies it is the exception not the rule. Most of my parents know that leaving the child with me in an emergency is actually better because I have everything the child needs and less for them to worry about.