I just wanted to add that young children really don’t understand the concept of the word “stranger”. In my opinion, you should tell your child not to go with anyone unless mommy or daddy tells them it is okay.
Why? A stranger might say to a child,“My name is ‘John Doe’. Now that you know my name, I am not a stranger to you anymore.”
Read article: http://life.familyeducation.com/stranger-safety/safety/53830.html
I agree with teaching your child not to go with anyone, regardless if they are strangers or not, unless mom or dad says it is ok. It is unfortunate that we live in a time when even those we think we know, may turn out to be a danger to our babies. I insist on knowing where my kids are at all times. I hate to be over-protective, but feel I have no choice these days. 
this is one of my greatest fear! :closedeyes: my son tends to be very friendly and he smiles to almost everybody!if the person in the lift with us is not smilling at him, he tends to catch his attention.he does not choose whom to go with which is why i am really very scared, i cant leave him unattended with the fear that someone might just pick him up.
how do we really educate our children about strangers?telling them that not to go with anyone unless its ok from mom n dad is still not enough, what else can we do?
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!
I still think that keeping a watchful eye on our kids ALL the time is the best way to prevent kidnapping. However we teach our children to ignore strangers, they all have weak spots which is almost certainly being leveraged by the strangers/kidnappers.
I agree that our kids do not understand the concept of strangers. I guess there is a certain age, maybe teenagers when it starts to register who a stranger is. I have an example, I was at the park with my son a few weeks ago and other older (maybe 7-9 year old) children were playing. A girl proceeded to ask me if I was a stranger. And my son was with me, so off course I didn’t want him to feel as if he was not welcome to play, he is only 2 and half. I said no we are not strangers, we are here to play. I had made it a point to teach my kids not to talk to go anywhere with strangers, just like my friends were teaching their kids. But do kids really understand who a stranger is? It dawned on me that this girls parents must have taught her about who strangers are, because she was asking me if I was a stranger. but she truely didn’t know what a stranger means. She didn’t know me, so in a way I was stranger, but how are our kids to know who is a good stranger and a bad stranger?? its tough.