Placebo, I agree with parents telling their children never to talk with strangers. Considering two children were taken outside of my school when I was a kid and were beaten because they followed a stranger when he offered them some sweets.
Children are far too innocent too be going out and talking to strangers. I think theirs a time when we're old enough and mature enough to go out and meet strangers and deal with them in a wise and safe manner. Until then children are made to be wary of strangers and for good reason as well. It's easy to trick a child. It's not very easy at all to trick or overpower a grown adult.
Jusy my two cents.