Police identified the deceased as Buddhi Bahadur Ale (8) of Benimadipur-2. He died while undergoing treatment.
Among the three injured, the condition of Man Bahadur Sunwai is critical. The other two, Yam Bahadur Sunwar and Nil Bahadur Saru, are said to be out of danger.
Meanwhile, a person who was critically injured in a road accident in Mahottari district on Sunday, died the same night.
The deceased is identified as Bharat Subedi (50) of Gaushala-7. A tractor whose number is not legible hit him at Ramnagar- 3, police said. He breathed his last while undergoing treatment at B&B hospital in Lalitpur.
According to the Area Police Office, Gaushala, the driver is on the run after the accident and the vehicle is under the police control.
Two persons killed in separate incidents in Saptari