According to police, the boy, Anshul Kumar, a resident of Gole Market in central Delhi, had gone to Lady Hardinge Medical College Tuesday morning with his parents to see his aunt.
He was kidnapped by Sunita from the hospital premises.
The duo's arrest followed a tip off to police about a gang of child traffickers.
"The gang would kidnap children and sell them, the boy was to be sold to a couple," a police officer said.
The police received information that Sunita would be coming to the central Delhi temple along with Kumar in the evening. A trap was laid and she was arrested. Her interrogation lead to the arrest of Anita a few hours later.
Meanwhile, another child, who was kidnapped by Anita two years ago and was staying with Sunita, was also rescued. Police are yet to ascertain the child's identity.
According to Anita, she was lured into the business by easy money and was promised Rs. 1 lakh for every child she could sell.