The link below is to an article in Yahoo News about a 5 year-old who crashed his van into his House and other property.
Yes - a 5-year old!
His mother was taking him skating and forgot the skates so she left the car running with him in it and when back into the house to get them. He got out of his car seat, moved into the driver's seat and put the car in reverse.
Fortunately, he wasn't hurt and the damage was minor but the story could have ended in any number of really terrible scenarios.
When will some parents learn that you NEVER leave a child alone in a running vehicle?