Read an interesting quote about this:

Psychologist Debrah Shulman said: "It's foolish to pretend to children that dangers do not exist. Children are aware of their vulnerability and are naturally concerned about their own safety. It's part of a parent's job to give them the tools to deal with danger realistically. If presented honestly and positively such information will not threaten children, it will reassure them." Yes, we have to talk to them about it.

I am only going on how i was taught when i was little, but my mum pretty much warned me that SOME strangers (even people i know) may try to take me or behave innappropriately and that i have every right to just scream as loud as i can and run away. She also just told me to follow my instincts and if i didnt feel comfortable to leave/run/tell someone. She also always said that Dad and Her would always try and protect me.

Maybe you can try reassuring DS that its not common that it happens but you want him to be prepared and aware because you love him so much...Maybe try and go through an action plan with him if something was to happen so he feels like he is in control.