This video is downright scary, showing a child abduction social experiment. I have also told my children never to talk to strangers and never to walk off with anyone but the problem is that children are trusting and when faced with something exciting like a puppy chances are so high that it may not occur to them to check with mom or dad first.
As you can see from this video it happens so fast and you can take your eyes of your children for just a moment and they can be abducted. Every parent should watch this video. This chap Joey has done a number of these types of videos, you should really watch a few of them.