You could tell your kids stories and discuss the with them simply afterwards... for example Hansel and Gretel is a great story for teaching kids not to go into houses of people they don't know, not to eat candy from people on their own...etc...
after the story discuss how its ok to eat something ONLY if they ask mommy first... so then they wouldn't put something in their mouths or go with someone unless they come back to you and ask first...
Make up stories like that that are a little bit scary but not too much and have a happy ending of the parents "rescuing" the children
And make sure to balance that out that it's ok to make friends with people their own age and ok to smile and talk to people when parents are around as long as they don't go anywhere with them unless they ask mom first...etc...
And most of all - just keep an eye on them from afar and notice when they are doing something right and asking permission and when they are not to teach them to take responsibility... and encourage them to tell you about their activities, their friends, their day etc... even in the most simple words... conversation should start from when they are very young even before they can say stuff that makes sense .. just to put them in the habit
hope that helps!