Bodies of Rajni Devi (27), her three-year-old son and his sister were found with severe burn injuries in their house.
Police said a probe was on to find out whether the incident was a case of suicide or murder.
The bodies were sent for post-mortem.
Rajni Devi's brother Rahul Kumar accused his sister's in-laws of burning her and her children to death.
He alleged that her sister was being harassed by her in-laws since her marriage to Abhimanyu Singh four years ago.