The woman, Irene Mbithe, was arrested on Thursday after residents of Kangurue slum in the capital Nairobi raised alarm over the suspicious death of her son, Brian Kibet.
When police arrived at the scene, the child's tongue and intestines had been pulled out in an attempt to "free him" from the said demons.
In a video posted on Youtube by K24 television, Brian's aunt Catherine Muthama expressed shock over the ordeal.
"Nilishangaa sana kufika hapa kuona mama mtoto amevuruta ulimi ya mtoto kabisa na nikamuuliza kwanini anamaiza mtoto (When I arrived I was surprised to see the mother having pulled out the tongue of the baby and I screamed at her asking why she had killed him," she said.
Neighbours said the exorcism went on the whole night on Wednesday, adding that the commotion in the house was abnormal.
The child's mother, who spoke in Swahili, maintained that she meant no harm to him.
"Mungu nifungwe kama kuna kitu kibaya nimetendea huyu mtoto wangu ambaye nimeombea sana kupata (God punish me if I have done anything wrong to my son who I love so much and have prayed for years to conceive and give birth to)," she said.
Police took Mbithe for questioning at the Kayole Police station while the body of the baby was taken to the mortuary.
Exorcism is defined as as a process or action that is used to get rid of an evil spirit.
Cases of exorcism are not new to Kenya.
Last year a man who was allegedly exorcised of a homosexual demon was picked up while swimming in Kenya's Coastal city of Mombasa. He claimed to have been given the demon by two men whom he swam with, according to Emmanuel TV.