Police said the boy child and his mother were released from the hospital in Burdwan earlier in the day and were on way home to Tamchini village in Memari area, about 20 km away in the rented car when the truck on the opposite lane smashed through the divider and rammed into the vehicle.
The driver of the car and the infant died on the spot and the vehicle's front was completely mangled under the impact of the collision.
The boy's parents and grandmother who were in the car were injured, the police said.
Local people broke open the car's door and extricated the bodies and rescued the injured, who were rushed to a nearby hospital even before the police reached the spot.
The truck driver and helper are absconding, the police added.
The couple has a five year-old daughter.