My parents are the same way, no matter how many times I have told them otherwise about pitbulls, they still think they live to attack children on the streets. They spent around 5 years or so living in a big city where there were reports of dog attacks atleast everyweek (so they say). They have got it stuck in their minds that they are vicious animals.
If I ever get the chance to introduce them to a real pitbull, I certainly won't pass it up. I'm determined to do my best to change their minds.