Sutheesh Kumar, a construction worker living in penury, had given the baby boy, his second child, to the couple on December 31 last after they lured him by offering Rs one lakh through a broker, they said.
He had agreed to the offer though his wife was not willing.
However, the couple did not take care of the baby properly and it started crying, following which neighbours informed police and Child Helpline officials.
A search was on for the broker, police added.