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

The correct answer is that all children under the age of 12 should be properly restrained in the backseat. This guideline is established to enhance the safety of young passengers in the event of a collision. The backseat is generally considered the safest position for children because it reduces their risk of injury from front-end crashes and also minimizes exposure to airbag deployment.

Research shows that children are significantly safer when seated in the back, away from the potential dangers posed by the front seat, including airbags which can deploy with considerable force. Proper restraint includes using age-appropriate safety seats, booster seats, or seat belts, ensuring they fit the child correctly for optimal protection.

While options like 5, 10, and 3 may reflect some common safety guidelines, they do not align with the broader recommendation to keep children under the age of 12 secured in the backseat, emphasizing the importance of prioritizing the safety of children as they grow.