According to the police, the incident took place in fish market in Mandawali area around 5.30 PM when the accused constable Ashok, who was on off-duty, was reversing his car when he hit Gopal and his grandmother.
Police said Ashok, who was in an inebriated condition, had come to the market with two other men.
"After the incident, both victims were rushed to a nearby hospital where Gopal was declared dead," a senior police official said, adding that the condition of the boy's grandmother is stated to be stable.