As the days following 9/11 turned into passing years, park rangers at the Flight 93 National Memorial began to face an unplanned challenge. Parents reliving the tragic day terrorists attacked the nation were approaching park staff, asking them to explain the sometimes dark, difficult subject matter in a way their young children would understand, park Superintendent Jeff Reinbold said. In most cases, the youngsters weren’t alive the day Flight 93 crashed, killing its 40 passengers, he said.