California Vehicle Code 27360 sets forth the main laws regarding the use of child restraint systems for drivers in California. California law only requires those 8 and under to ride in back seat.The 10 year old can legally ride in the front. In California, it's the law: All children under the age of 8 must be secured in a car seat or booster seat in the back seat. (California Vehicle Code Section 27363.) Passengers who are 16 years of age and over are subject to California's Mandatory Seat Belt law. The law states that children over the age of 12 or 135cm in height can use a booster seat. All children at least 4 years old (but younger than age 8) must ride in a child passenger restraint system or booster seat, unless they are taller than 4'9″. Kids 6 and up or those heavier than 60 pounds can use just an adult seat belt. California car seat laws and booster seat laws. Children under age 8 must ride in the back seat in either a car seat or a booster seat.