The pilot was taking a group of mentally retarded children for a flight. On the first flight one of the children became distressed and the flight was terminated. On final approach for the first landing of the second flight, the child seated behind the pilot became hysterical and grabbed the pilot around the throat. A missed approach was carried out and another circuit completed. As the aircraft approached for landing the child again became agitated. The pilot reported that he was concerned about the situation and lost concentration during the approach. The aircraft ballooned and landed heavily.
