"Navina Sanjay Rande gave poison to her son Yuvraj on Saturday morning before eating it herself," said Inspector Sunil Gaonkar of Talasari police station.
He said that the woman had lost her husband in a road accident around one year back and used to do domestic work to earn living.
The bodies of the woman and the child were spotted by neighbours who then informed police.
Gaonkar said they were conducting investigation to find out the motive.