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What are California's booster seat requirements by age, height, and weight in 2025?
Executive summary
California’s baseline law in 2025 still requires children under age 8 (or under 4′9″) to be secured in a car seat or booster in the back seat (California Vehicle Code §27360) [1]. A high-profile legislative push in 2025 (Assembly Bill 435) sought to extend size‑based rules through the teen years by adding a five‑step seat‑belt fit test for children 8–16 and to change front‑seat placement rules; the bill was negotiated and a version was signed that phases in additional rules by 2027, including the five‑step test and potential fines if a child’s belt does not fit properly [2] [3] [4].
1. What the law said in 2025: the standing baseline
Through 2025 the clear statutory baseline is that children under age 8 must be secured in a child safety seat or booster and should ride in the back seat; manufacturers’ height/weight limits apply for specific seats [1]. Multiple 2025 summaries and state guidance reiterate the familiar threshold: under 8 years old or shorter than 4′9″ is when a child must remain in a child passenger restraint system under California law [5] [1].
2. What changed (or was enacted) in the 2025–2027 legislative push
Reporting shows lawmakers passed a revised version of Assembly Bill 435 that was signed by the governor in 2025 but whose operative elements begin in 2027. That enacted change does not simply raise a single age or height; instead it adds a statewide, five‑step seat‑belt fit test that applies to children ages roughly 8–16 to determine whether they can safely use an adult seat belt without a booster [2] [3]. Several outlets indicate the signed law was a “watered‑down” version of earlier proposals that would have banned short teens from front seats and raised mandatory booster ages [2] [6].
3. The five‑step test: what reporters say it requires
Media summaries list the five questions drivers must be able to answer “yes” to about a child’s belt fit — for example: child sits all the way back; lap belt low on hips/thighs; shoulder belt across chest/collarbone; child can stay seated throughout the trip; and likely one about knees bending at the seat edge — and if the driver cannot answer all affirmatively the child should remain in a booster [2] [3]. Enforcement and fines are described in those reports (a cited $490 fine appears in some reporting for failing the test when driver cannot answer yes to all five), although exact fee schedules vary among stories [3] [4].
4. Age vs. size: the policy shift and rationale
Advocates and several safety groups emphasized that size — not age alone — determines when a child can safely use an adult belt; the California Highway Patrol, AAA, NHTSA, the California Department of Public Health and pediatric groups promoted the five‑step fit approach as aligning with safety science [7] [8]. Opponents and some legislators warned the measures could be burdensome or impractical (e.g., pickup‑cab concerns, cultural/back‑seat traditions), which led to the bill’s modifications before final signature [8].
5. What parents need to know in practice (2025 context)
As of 2025 parents must keep under‑8 children in appropriate restraints and follow manufacturer weight/height limits [1]. Beginning when the new law takes effect (reporting says January 1, 2027, in several pieces), children ages 8–16 will be assessed under the five‑step test and may need to remain in boosters until the belt fits correctly; adding a booster often fixes fit problems without changing statutory age rules [4] [3]. Available sources do not mention detailed enforcement protocols for every locality or all exact fine schedules beyond the reported examples [3] [4].
6. Conflicting or clarified claims in reporting
Some stories suggested the law would force 13‑year‑olds into boosters or ban teens from front seats; later reporting and explainers clarify the final law centers on the five‑step fit test and does not automatically require boosters for every teen — it requires proper belt fit whether achieved with or without a booster [4] [6]. Reporters and fact‑checking pieces explicitly note the common misunderstanding: the law is size/fit based and phases in in 2027 rather than instantly upending the 8‑or‑4′9″ baseline [9] [4].
7. Bigger context and unanswered details
Safety advocates frame this as aligning law with NHTSA/AAP guidance that a booster should be used until an adult belt fits properly; legislative supporters argued it would reduce injuries among smaller youth [5] [7]. Available sources do not mention the full text of AB 435 here, exact statutory language for each enforcement scenario, or every municipality’s enforcement plans — for those specifics, the bill text and official state vehicle‑code updates should be consulted (not found in current reporting) [2] [1].
If you want, I can pull the precise five questions as quoted in a single source and summarize the exact penalty language that reporters cited so you can see the test and the fines side‑by‑side (pick a source preference from CalMatters, LAist, or CHP).