Deputy Superintendent of Police Dilnawaz Ahmed said the incident happened in a village falling under Bahadurpur police station area of the district.
The minor girl Archana had, while preparing tea, mixed pesticides mistaking the packet for one containing tea leaves resulting in the tragedy.
Three members of her family Dukhan Mahto (60), Ramswaroop Mahto (65) and Archana herself, fell sick and died at home itself.
The fourth victim Prakash Mahto died during treatment at hospital, the DSP said.