The incident took place this afternoon in Daraganj police station area, a stone's throw from the famous Nagvasuki temple.
A six-year-old boy and two girls aged four and ten years respectively were injured when one of them picked up a crude bomb lying abandoned in a heap of refuse and apparently tossed it mistaking it for a cricket ball, police spokesman Gyanendra Rai said.
He said the bomb, which appeared to be of very low intensity, went off after falling on the ground causing minor injuries to the children who returned to their homes after getting first aid at a clinic nearby.
"It appears that some anti-social elements might have inadvertently dropped the bomb while being chased by police", he claimed.
Meanwhile, panic gripped the city for some time as news of the explosion spread bringing back memories of the ghastly incident of May 23 when a powerful explosion had ripped through a congested slum in Kareli police station area, about 15 kms from the site of today's blast.
The Kareli blast had claimed the lives of five children and injured six other people.
The case is being investigated by Anti-Terrorist Squad of Uttar Pradesh police.