ON 6/12/17 I BACKED OUT OF MY GARAGE AND SHIFTED THE TRUCK INTO PARK.(ELECTRONIC ROTARY DIAL SHIFTER MOUNTED ON DASH) I EXITED THE TRUCK TO RETRIEVE AN ITEM IN THE GARAGE, LEAVING THE TRUCK RUNNING. MY 10 YEAR OLD SON, WHO WAS INSIDE THE TRUCK, SCREAMED TO ALERT ME. I OBSERVED MY TRUCK IN MOTION MOVING FORWARD TOWARD MY GARAGE.(NOT COASTING AS IF IT WERE IN NEUTRAL BUT RATHER IN DRIVE). I ATTEMPTED TO GET BACK INTO TRUCK TO APPLY BRAKE BUT WAS UNSUCCESSFUL. THE TRUCK IMPACTED THE EXTERIOR OF MY GARAGE BETWEEN THE DOORS WITH MY SON INSIDE THE TRUCK. HE WAS SEAT BELTED AND UNINJURED, PHYSICALLY. UPON ENTERING THE TRUCK I OBSERVED THE GEAR SELECTOR TO BE IN PARK. I IMMEDIATELY SHIFTED INTO REVERSE BACKING UP APPROXIMATELY 15-20 FEET. I SHIFTED THE TRUCK INTO PARK AND AGAIN EXITED THE TRUCK TO SURVEY THE DAMAGE. THE TRUCK AGAIN BEGAN MOVING FORWARD AS IF IN DRIVE. I WAS ABLE TO APPLY THE BRAKE REACHING IN WITH MY HANDS TO DO SO. I AGAIN OBSERVED THE TRANSMISSION TO BE IN PARK. I SHUT THE IGNITION OFF AT THIS POINT. IMMEDIATELY FOLLOWING THIS EVENT I ATTEMPTED TO REPLICATE IT IN MY DRIVEWAY APPROXIMATELY 20-30 TIMES, SHIFTING FROM DRIVE TO PARK AND LETTING MY FOOT OFF THE BRAKE. I WAS UNABLE TO REPLICATE IT IN THESE ATTEMPTS. MY TRUCK SUSTAINED JUST OVER $3,000 WORTH OF DAMAGE. I HAVE NOT AT THIS TIME GOTTEN AN ESTIMATE FOR THE DAMAGE TO MY HOME. THE MAJOR CONCERN I HAVE PERTAINS TO THE FACT MY SON WAS INSIDE THE TRUCK AND MY DAUGHTERS PLAYING NEARBY WHEN THIS E