I don't care if my kids do not respond when some one asks them their name or how old they are. I feel that by them chosing not to respond, they are showing their inpendence in a manner that they don't like something about that particular person.
I would rather have a child who acts shy or even a little rude around people they don't know than have a child go missing because they were polite and chatty with the local kid napping store clerk.
I never let my kids leave my sight, even when we are at home, they are to only play in the fenced in backyard, if I am busy in the house.