Police said Sonu went missing around 11.30 am and was found from inside a Honda Accent car parked outside his home around 4 PM.
It is suspected the child entered the car accidentally and could not open it to come out, they added.
The owner unlocked the car around 4 PM when he found Sonu inside the car and informed the police.
Sonu was rushed to a hospital where he was declared brought dead.
Milind Dumbere, Deputy Commissioner of Police (Northwest), said they are probing the matter from all angles.
The boy's parents sell items on a cart.
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