I think children need to know how to be social. The more people they come across in different situations will hopefully help them develop their own "stranger radar". We need to respect as parents if a child does not want to go to someone, so we don't suppress that radar. I know as kid I was often forced to be social with men that just creeped me out, otherwise I being rude.

Really most people are fine, if anything if your child is lost, it will be an adult they will need to approach to ask for help. Maybe teach them who is safe to approach in that situation, like the lady at the service counter at the supermarket for example.