As of September 2023, the California Car Seat Law, which is part of the California Vehicle Code, requires the following for child passenger safety:

1. Rear-Facing Car Seats:

   - Infants under the age of 2 or those who weigh less than 40 pounds must be secured in a rear-facing car seat in the rear seat of the vehicle. 

2. Forward-Facing Car Seats:

   - Children who are at least 2 years old or who have outgrown the rear-facing car seat's height or weight limits must be secured in a forward-facing car seat with a harness in the rear seat of the vehicle.

3. Booster Seats:

   - Children who have outgrown the forward-facing car seat but are under 8 years old or are under 4 feet 9 inches tall must be secured in a booster seat in the rear seat of the vehicle.

4. Seat Belts:

   - Children who are 8 years old or older or who have reached 4 feet 9 inches in height can use the vehicle's seat belt system. However, it's recommended to keep children in a booster seat until they properly fit in a seat belt without it.

It's important to note that these requirements may have changed since my last update. Car seat laws can vary by state, and they can change over time. Therefore, it's crucial to check the most current California car seat laws and guidelines from the California Department of Motor Vehicles (DMV) or consult with a local law enforcement agency to ensure you are complying with the latest regulations.