The bodies of Rahul (10) and Ankit (6) were found in a field yesterday while 8-year-old Anjali was lying injured beside them, police said.
The children, who studied in a school at Albatia area of Agra, were allegedly picked up by their uncle Tarachand on Thursday.
Yesterday, two of them were strangled to death while Anjali was also attacked, police said.
Anjali was sent to Agra for treatment where her condition is stable.
"The bodies of Devi Singh's sons were taken to Dauki town by relatives to be cremated there," said Uday Pratap Singh, SHO, Jagdishpura.