Yash was sleeping in a room with his father Lalit when a bullet fired through a window hit him on his head.
From preliminary investigation, it has emerged that Lalit was the actual target, police said.
Accused Vinod, husband of the victim's maternal aunt, was allegedly involved in a dispute with Lalit, police said.
The incident was reported around 10 PM yesterday and Vinod left the sight of crime and left in a car from there, which was driven by another person.
Today, police tracked down the car and arrested the driver, identified as one Ashok.
"We are questioning Ashok, who has disclosed that he dropped Vinod at a specific location and several teams are looking out for him," DCP (West) Pushpendra Kumar said.