Can a child under 12 years old and shorter than 135 cm travel in the front seat of a private car without a child restraint system?

Why this is the correct answer

Children under 12 years old must travel in the rear seats using an approved child restraint system (SRI). The key rule in Spain is based primarily on HEIGHT, not age: a child restraint system is legally required for any child measuring 135 cm or less. A child under 12 who is EXACTLY 135 cm tall — or taller — is no longer required to use a child restraint system and may exceptionally use the vehicle's seat belt directly, even in the front seat. However, Spanish traffic authorities strongly recommend continuing to use an appropriate booster seat until the child reaches 150 cm, since the standard adult seat belt is not designed for smaller body frames. In all cases, the shoulder strap must cross the collarbone and chest (not the neck), and the lap belt must sit low over the hips. If the shoulder strap touches the child's neck or chin, a booster seat should still be used. Penalty for non-compliance: €200 fine and 4 penalty points.