All children under the age of ____ should be properly restrained in the backseat.

The appropriate guideline states that all children under the age of 12 should be properly restrained in the backseat to ensure their safety while traveling in a vehicle. This recommendation is based on research indicating that the backseat is generally safer for younger passengers, as it reduces the risk of injury during collisions. Children are particularly vulnerable to various risks in the event of an accident, and proper restraint systems, such as seat belts and child safety seats, are essential for minimizing these risks.

While the other age options presented may have different guidelines for specific restraint types, the best practice widely recognized by safety organizations and traffic laws is to keep children under 12 in the backseat, as it provides maximum protection in the event of a crash. This reflects a commitment to child passenger safety and responsible driving practices.