Children under the age of 8 must be secured in a car seat or booster seat in the back seat. Children under the age of 8 are required to be secured in a car or booster seat."Children must be in a proper child restraint (booster seat or safety seat) until they reach at least eight years old, and this law applies to the backseat. The booster seat laws in California require kids to use a booster seat or harnessed car seat if they are below the age of eight. California law only requires those 8 and under to ride in back seat. The 10 year old can legally ride in the front. California law requires a child to be 8 years old to ride in the front seat. Children to be correctly restrained in a car seat or booster seat until they are 8 years old OR 4'9" tall. According to California state law, children under eight years of age must be properly secured in a car seat that suits their weight, age, and height. The State of California also has certain regulations relating to the use of booster seats.