Pooja and Sachin tied the hands and legs of Lalit before they pour kerosene and set him on fire.
Lalit's mother, who was out of the house when the incident took place, got a phone call about the incident and rushed home only to discover the charred body of her son.
Superintendent of Police Maan Singh Chauhan said before being set on fire, the child was badly beaten. An empty tin of kerosene was also recovered.
Police said the reason behind the incident was not immediately known. A hunt has been launched to nab the duo.
Police said that Sachin used to visit Pooja's house frequently.