Reshma, the alleged child trafficker, Jalil (43) and his wife Maimuna were arrested on a tip-off, they said.
A police team found the three walking on a road with a boy. When questioned, Reshma confessed that she had found the child six months ago at the Arsikere Railway Station and had sold him to Jalil and Maimuna for Rs 90,000.
Jalil, Maimuna and Reshma were arrested under Section 370 (buying or disposing of any person) of the Indian Penal Code and produced before a city magistrate court, which remanded them to judicial custody.
The police produced the child before the Child Welfare Committee, which sent it to a care centre in Puttur.
Further investigations were on, police added.