I was so proud of my ten-year-old niece who was riding her bike when a man in a car slowed down and asked her something. She didn't stop to find out what it was, but rather took off on her bicycle as fast as she could and the guy pulled away. In light of this story it makes me weak thinking about what might've happened had she stopped to talk to him. I commended her for her quick thinking, and believe that it's important for the adults in a child's life to help them set good boundaries between them and strangers, and even people they know, if they have any reason to doubt their actions or motives.
It's a good idea to tell the child to run or bike in the opposite direction that the car is heading.