The incident took place early this morning in Nakphula village under Kotwali police station, Superintendent of Police Mohit Gupta said.
The victims were identifed as 18-year-old Zamir, 12-year-old Salman, and 1-year-old Sahil, Gupta said.
Two other persons, present in the house at the time of the incident, suffered minor injuries, he said.
Senior officials rushed to the spot on getting information and all the bodies have been sent for post-mortem, he added.