Sadly, the perverts are so tricky and the kids so innocent that it's hard to drill it into their heads to be afraid of EVERYONE.
My girlfriend's 9 year old was walking home from the school bus one day. She wanted to be a "big girl" and not have my friend walk with her, but my friend could see out the window and watch the whole walk. One day she was watching and a car pulled up to her daughter about 1/2 a block away from the house - the bus stop was only about 1-1.5 blocks away from the house - and she watched in horror as her daughter started talking to this person. It was a small neighborhood in what then was a small town so my girlfriend knew it wasn't anyone from the neighborhood. My friend ran outside and started calling her daughter and the man in the car sped off. My friend went running to her daughter just freaking out "We've had this talk so many times - you're not supposed to talk to strangers!". Her daughter was in tears and said, and I'm sure it was 100% the truth "I forgot.".

Just that one second could have cost her her life and/or worse.
I remember seeing that show on Oprah where the parents had been talking to the kids for years, and even impressed AGAIN in front of the cameras that their kids shouldn't talk to strangers. But almost every single time, when faced with the actual situation, they did.
My son had my nieces baby picture on his website with her name on it and my brother freaked out. At first I thought he was over reacting, but then again......
I can remember riding my bike for MILES to get to stores, the pool, the orthodontist, etc. and that was in a relatively large town - Jacksonville. Nowadays, there's NO WAY anyone would send an 11-15 year old girl out on major roads by themselves.
Honestly, I couldn't have kids at this age - I'm too old for all the panicking and worry!