The problem with never talk to strangers is that if a child needs help, or is lost they are afraid to ask anyone for help. I have had this happen to me twice, where I found a lost child, one in a parking lot, one in a store.
They were both young and scared to death, but ran away from me because they looked at me as a stranger.
It is a better approach, IMO, to teach children to look for someone they can trust to help them, know when to avoid strangers and what to say if one does approach them.
the book I recommend above gives the example of "look for a Mommy", because chances are that a woman with children is going to help a lost child. Of course not in every single case is that true. But I think it is better than Never, ever talk to strangers.
Just my .02. It is a scary world out there, sometimes, for those of us with young children. We all do the best we can to protect them.
It is a problem and a hard one to explain to young children. There is a huge difference between a stranger approaching a child and a child approaching a stranger. If a child who's needing adult help approaches a stranger, chances are that stranger will be a "good" person. If a child must choose between a woman and a man stranger, instruct them to go the the woman. Nothing against all the good men out there, but "stranger danger" women are almost unheard of. Better yet is the mother with children in tow.