The incident took place in Jani Khel area in Bannu district of Khyber Patkhunkhwa bordering north Waziristan Agency, police said.
The house suddenly caught fire at Janikhel, killing two children, mother and grandmother, said Muhammad Zaman, SHO Janikhel police station.
He said fire broke out and engulfed a room of the house which the victims were sleeping in and had been used to store petrol for firewood for the harsh winters.