This is good advice. ^ It helps to focus the conversation on boundaries rather than fear/danger. When I'm at the playground I expect my children to ask me if it's okay to go play with another kid or talk to someone new. Same thing if someone offers them food, gives them a toy, knocks on the door, etc. Even if it's someone we know! If we're out somewhere and they do something without asking me first, we immediately leave. You won't have to do this more than once in most cases — they get the picture!
Reply to Stranger Danger