Kusum, 14, Kanchan, 10, Rohit, 6, and Mohit, 5, were burnt alive and Kirpal Singh and Surajwati were injured when a fire broke out in their house in the fields of Mohammadpur village, near the Delhi-Gurugram expressway.
Singh, hailing from Badaun district in Uttar Pradesh, does farming on nearly 4 acres of land on a contract basis.
He has been referred to Safdarjung hospital in Delhi as his condition is said to be critical, a relative of the victims told IANS here.
The reason behind the blaze could not be ascertained immediately.
The bodies have been sent for postmortem.