Kilauea, on Hawaii's Big Island, is one of the world's most active volcanoes.
It routinely erupts, and the latest eruption began on 23 December with lava pictured gushing to the surface.
The eruption is continuing at a low level within a closed area of the national park, the USGS Hawaiian Volcano Observatory said in its latest update on Saturday.
The park said the incident happened on Christmas Day in a closed area of the park where families had gathered to watch the lava.
It was in an area overlooking the caldera - the large crater of the volcano - and the boy would not have survived the fall, Ms Ferracane said.