Five children, aged between five and ten, drowned in a large pit filled with floodwater on Monday, an official said.
District magistrate, Katihar, Punam said the incident took place in Bochahi village falling under Narayanpur panchayat of Manihari block.
The children, including two girls, slipped into the pit while playing, she said.
Punam said all the dead were adivasis (tribals) and members of the same extended family.
The total number of deaths due to drowning in floodwaters in the last 24 hours in Katihar has reached 10, the district magistrate said.
Five people, including four minors, had died in four separate incidents on Sunday, she added.
Ex-gratia of Rs 4 lakh will be given to the next of kin of each child who died in line with the state government's policy, Punam said.
According to the State Disaster Management Department, Katihar is among the 13 districts in Bihar which have been hit by floods caused by torrential rainfall a week ago.