The incident occurred at 7.30 AM when the driver of the school bus lost control over the bus and it overturned, SHO, Bhaltha Police Station, Nand Kishore Nager said.
Phool Singh, Rakesh and Rajiv, aged between 8 and 10 years, and bus cleaner Ismile were killed on the spot.
22 children were injured, five of them critically. The injured were rushed to a government hospital in Jhalawar where they are undergoing treatment.
According to the bus driver, he lost control over the vehicle after brakes of the bus failed.