According to a study made by University of Michigan Transportation Research Institute, “the primary impact is between the vehicle and another object, while the occupants continue to travel forward at the precrash speed. Unrestrained occupants then come to an abrupt stop against the decelerating vehicle interior or the ground outside the vehicle.
Restrained occupants collide with their belts, or other restraint system, very soon after the primary collision. Finally, there are collisions between the body’s internal organs and the bony structures enclosing them, which can be mitigated by the use of occupant restraint systems.”
Now with this data, imagine the effect on an underdeveloped and really soft body of a child. Without the proper restraint, you basically reduce the chances of a kid surviving any vehicular accident to zero every time you place him or her on the lap of the mom or yaya, or alone in the backseat.