We have recently introduced a safe word for each of our children (aged 11 and 7) to get round the difficulty of strangers v friends v acquaintances. If anyone other than immediate family tries to pick them up from somewhere or take them somewhere, the children are not to go unless the adult tells them our safe word that can only be given by us as parents.
If used, we can reset the safe word. We are hoping that this gets round the issue of the friendly neighbour up the road trying to take them somewhere, or the teacher (who it is OK to go with in school, but not out of school time) offering them a lift etc.
We never insist that our children kiss ANY relatives goodbye, or us if they don't want to, to try to avoid feeling uncomfortable but "doing as you're told" etc. We talk about not keeping secrets, always talking to us, not going with anyone (even family) if you're not comfortable.
If we are on big days out they have our mobile phone number (wrist band / paper) and are told not to go anywhere with anyone. A kind adult would understand that, and help without making them move.
When they asked what someone would do to you, I asked our children what they thought, both said the worst thing they could think of and I agreed that "it's the worst thing they could think of", hoping not to scare them and to protect their innocence.
Then I think it's case of take a deep breath and let them grow up not feeling scared of everyone !!