You can screen the video before you take them to a seminar.
As for keeping them innocent, well, that's a different issue. Also, it's not always strangers who could hurt a child, most of the time it's someone who has befriended the child or their parents.
ES mostly applies to older kids, I can't see you allowing your son to play alone. I don't let my kids play outside alone, and mine are much older than your son. It should be a must for any child who goes to school.
Anyhow, it teaches the kids what to do if they are pulled into someone's car, how to run away from someone trying to abduct them, if they are taken to a hosue how to get attention of the police and others, how to clog a toilet in order to get the abductor to be busy so they can escape, etc.
Samten - I dont think being non-verbal will have an effect on how he takes to the movie, but I think your son would be a bit too young yet. You certainly could try and even introduce the concepts now.
dont know - a person you dont know
kinda know - someone you kind of know
safe side adult - an adult they can trust (they need 3)
safe space - basically personal space no don't or kinda know needs to be in.
HTH,
meg