Cousins Sonu, 5, and Raj, 6, were found in a cab owned by the family in the Ranhaula area in outer Delhi. There were burns on their bodies.
The cab was reportedly owned by the father of one of the boys.
The cab driver, Raju, lived with the family and on Wednesday afternoon, allegedly left the car unlocked when he went to his room to sleep.
The police say on realizing that he had left his car unlocked, he remote-locked it using his key.
The police believe that the car was still cool as it hadn't been long since the AC had been switched off, and the boys fell asleep.
A few hours later, their parents started looking for them and called the police. At first, the police as well as the family suspected that the boys had been kidnapped.
When the family took out the cab to expand their search, they noticed the two children on the floor in the back. The boys were rushed to the hospital but it was too late.