The 26-year-old woman, who also has a six-year-old son, had left her husband some time back due to a misunderstanding and come to Rasipuram, where she reportedly developed a relationship with an autorickshaw driver, police said.
The incident came to light when the boy's school teacher on noticing burn marks all over his body questioned him yesterday.
She then took him to a hospital and later to a police station, where he again narrated what had happened.