I PULLED INTO DRIVEWAY AND PUT CAR IN PARK, LEFT ENGINE RUNNING. WENT TO DOOR OF RESIDENCE TO GET MY KIDS. KIDS WENT OUT TO THE CAR AND WERE YELLING FIRE! I SEEN THE INSIDE UP IN SMOKE. I REACHED INSIDE TO TURN ENGINE OFF. WE THEN STARTED POURING BUCKETS OF WATER INTO SEAT AND ON FLOOR AROUND THE SEAT TO TRY TO PREVENT SPREAD OF THE FIRE. I LUCKILY PUT THE FIRE OUT. FIRE DEPT UNHOOKED BATTERY AND REMOVED MELTED PLASTIC AROUND SEAT. IT SEEMS A WIRE SOMEHOW SHORTED OUT BENEATH SEAT AND CAUGHT THE SEAT AND FLOOR ON FIRE.