Six year old girl was sitting in her dad's lap driving the boat. 6-yr old unexpectedly pulled the throttle back to near idle from a 20 mph speed causing her 8year old sister to lose her balance and fall over the front of the rail of the pontoon and become injured. Officers stated that near the end of September 2013 the officer began to hear rumors about a boat accident on Lake Murray involving a child that was airlifted to the hospital. The officer got a name and contacted the mother of the injured child. The officer set up a meeting on October 6, 2013 with the mother, and the father. They Gave statements as to what happened and I went to the location that the boat was kept and took pictures. Apparently the injured 8 year old child fell over front rail of the pontoon after the throttle was suddenly and unexpectedly cut back to near idle from approximately 20 miles and hour. Victim's 6year old sister, was sitting on her fathers lap driving the boat. Operator said that he pulled the throttle the rest of the way to neutral after he saw his daughter, Victim, fall over the front rail of the pontoon boat. The boat was turned around and operator jumped into the water and help Victim, who was wearing a PFD, back into the boat at the swim ladder. This is when he noticed the cut on the back side of Victim. She was wrapped in a towel and they headed back to their house on the lake. EMS responded and took Victim o a waiting helicopter to take her to Palmetto Health Richland. There was a deep laceration on Victim's upper buttock and a cut on one of her toes that was also broken. the offficer is not sure whether the victim was struck by the propeller.