Whether you live in California or you are visiting, knowing your car seat laws is important. When you are visiting and renting a car to go around, it is important to know the safety standards and regulations that apply on child safety seats and booster seats. California’s Car Seat Laws Seatbelt. Any operator of a motor vehicle must wear a seatbelt at all times; needless to say, all vehicles must have functioning safety seatbelts. Children older than 8 who are at least 4 feet 9 inches tall can.