The number killer of young children in the US is traffic crashes which were not restrained at all?
The NHTSA also reports that children who are unrestrained are 70% more likely to be killed in a crash than children who are properly restrained. Additionally, children who are seated in the front seat are three times more likely to be killed in a crash than children who are seated in the back seat.
For these reasons, it is important to ensure that children are properly restrained in a child safety seat, booster seat, or seat belt every time they ride in a motor vehicle. This can significantly reduce their risk of injury or death in a crash.