The boy of little more than 2 years was allegedly beaten up by the therapist following which, he received injuries on his head and back at her clinic on Anwar Shah Road on Monday, a Kolkata Police official said.
"We have arrested the therapist yesterday after going through the CCTV footages of her clinic," the officer said.
Following the assault on the child, his parents had taken him to a hospital.
The boy's parents then lodged an FIR against the woman at the Charu Market Police station, the investigating officer said.
She was arrested under provisions of the Juvenile Justice Act a local court today remanded her to judicial custody till May 19, he added.
"Our child is under severe trauma. We do not want anybody to come across such a therapist who can be so inhuman to a child," the boy's mother said.