WHILE PARKED WITH ONE WHEEL BEHIND PARKING STOP, A/C RUNNING AND VEHICLE THOUGHT TO BE IN PARK, VEHICLE SAT THERE FOR 5 OR MORE MINUTES, VEHICLE STARTS MOVING FORWARD,GOES DOWN ABOUT 8'SLOPE, ACROSS ROAD, DOWN ANOTHER 14'SLOPE, THROUGH FENCE TAKING UP 4/4 POST SET IN CONCRETE, STRAIGHT AS ARROW ABOUT 100 PLUS FEET INTO LAKE. MOTHER AND STRANGER WERE ABLE TO OPEN DOORS AND REMOVE TWO CHILDREN BEFORE CAR SUNK TO TOP, WHEN WRECKER GOT CAR OUT IT WAS IN REVERSE, AND THE DOORS OR WINDOWS WOULD NOT OPEN.*AK