Children under 12 years old and shorter than 135 centimeters must use **child restraint systems** appropriate for their height and weight. These systems are essential for their safety and must be properly secured in the rear seat of the vehicle.

- **They cannot travel in the front seat** of a passenger car without an approved restraint device, except in exceptional situations such as when the vehicle has no rear seats, all rear seats are occupied by other children, or it is not possible to install the restraint system in the rear seats.

- Standard seat belts are not suitable for children of this height, as they do not provide the necessary protection. Therefore, it is crucial that they use an approved child restraint system.

In summary, a child under 12 years old and with a height of 125 cm cannot travel in the front seat of a passenger car without an approved restraint device, as this is fundamental for their safety.