Superintendent of Police Ashish Bharti said that the incident occurred when Mahboob Alam, a property dealer, and his son Tabrez Alam were having sugarcane juice at Bata Chowk.
Three unknown men came there on a motorcycle and fired at them killing the child on the spot and injuring his father and the sugarcane juice vendor Sanjay Manjhi, he said.
The assailants then fled from the spot.
The injured were admitted to Munger Sadar Hospital but the police were unable to get any information from them as both were unconscious, Bharti said.
The attack could be the result of old enmity, the SP said adding the police were taking the help of CCTV footages to catch the culprits.