The elephants had gone to the village, about 45 km from the district headquarters, in search of food. Since paddy was stored in house, the animals pulled down the house at about 3 am when the victims were sleeping.
The two children died on the spot and their grandmother was seriously injured, Divisional Forest Officer (DFO) Saurabh Chandra said.
The victims were identified as Sanjit Malhar(5), son of Binod Malhar, and Chintamani Kumari (12), daughter of Kisto Malhar. Their injured grandmother Kumudni Devi (50) was admitted to the Patliputra Medical College Hospital.
The forest department has sent two teams to the village to drive out the elephants, officials said, adding that prior to the incident 18 elephants were seen moving around the neighbouring areas for the past six days.