New California Law Says Your 15-Year-Old May Need a Booster Seat — California Says So

California’s New Seatbelt Law Redefines “Properly Restrained” — Even for Teens

(CLAIR | Simi Valley, CA) — A new law passed by the California Legislature changes how the state defines what it means for a child or teen to be “properly restrained” in a car — and it’s raising questions from parents, police, and school officials across the state, including in Simi Valley.

Assembly Bill 435, signed into law in October 2025, introduces a new “5-step test” that must be met for any passenger under 16 to be considered legally buckled with a standard seatbelt. The law takes effect January 1, 2027.

Under the new standard, an older child or teen must:

• Sit all the way back against the vehicle seat
• Bend their knees comfortably at the edge of the seat
• Have the shoulder belt cross the center of the chest and shoulder
• Have the lap belt rest low on the thighs, not the stomach
• Be able to stay in that position for the entire trip

If a child or teen under 16 doesn’t meet all five points, they are not considered legally restrained — even if they are wearing a seatbelt. In that case, they would still be required to use a booster seat.

What Changes
Previously, California law allowed kids to stop using booster seats once they turned 8 years old or reached 4 feet 9 inches tall. This new law overrides that — focusing on how a belt fits, not just a child’s age or size.

That means 10, 12, and even 15-year-olds who don’t pass the fit test may now be required to continue using booster seats.

Enforcement Challenges
The law doesn’t increase fines but does redefine who is in violation. It also raises enforcement questions. Will officers be expected to judge leg position and belt alignment at traffic stops? Will a fidgeting teen in the back seat put a parent at risk of a ticket?

Safety Evidence Limited
While the law is based on guidance from safety organizations, there is little publicly available data showing that teens or older children in seatbelts have died in crashes due to failing this specific belt fit test.

In fact, no case in California from the past 20 years clearly documents a fatality involving a child over 10 who was wearing a seatbelt but would have survived if the belt had met the five-step criteria.

Local Concerns
For Simi Valley families, the law raises several questions:

• Do parents need to buy new booster seats for kids who stopped using them years ago?
• How will schools and buses handle the new fit rules for teens in district vehicles?
• Will this change focus attention away from more urgent safety issues — like distracted driving or speeding in school zones?

The law takes effect in 2027, giving state agencies time to issue enforcement guidance. But for now, many parents and local leaders are asking whether this new standard goes too far — especially for families already doing their best to keep their kids safe.