The couple and the infant were sleeping inside their house in Shiv Colony when some persons threw acid at them in the wee hours, they said.
Baldev Singh, aged 32, his wife Karamjit Kaur (30) and their child were rushed to the Sonepat Civil Hospital, police said.
Later, they were referred to PGIMS, Rohtak, for further treatment.
The family hailed from a village in Kaithal district and were currently residing at Sonepat, police said adding a case had been registered in connection with the acid attack.