When to Switch from a Car Seat to a Booster Seat

Over the past few weeks we've noticed that our 4-year-old seems to have outgrown her car seat. She still fits it, but the straps are getting tighter and harder to adjust, and as a fairly tall kid she's looking a little silly in the car seat.

We've been using Britax Marathon car seats for both children. They're expensive, but we definitely got our money's worth out of them, and they can be used for kids up to 65 pounds. They're also easy to install, which is a big plus, given that it's estimated that 80–90% of all car seats are improperly installed, which definitely has an impact on their ability to a child safe in a collision.

The big difference between car seats and boosters are that the booster raises the height of the child so that she can properly use the car's lap and shoulder belts. (The new one we bought has a bunch of nifty accessories, too, like reading lights, cup holders, and snack trays.) Unfortunately, it's kind of confusing as to exactly when you can start using the booster seat. The manufacturer says 3 years old or 35 pounds, while California law only states that they need to be in a car seat or booster until age 6 or 60 pounds.

Fortunately, the American Academy of Pediatrics manages to clear things up on its HealthyChildren.org website, where their car seat section answers just about any practical question you may have about car and booster seats. Basically, children should ride in a forward-facing car seat with a harness (like the Britax Marathon) in the back seat until they're 4 years old. Even at 4 and older, children should be big enough to actually fit in the booster, based on the minimum height and weight requirements stated in the booster seat instructions. So if your child still isn't big enough, stick with the car seat for a while longer.

As I mentioned earlier, it's really important that all car seats are installed properly, otherwise their safety is comprimised. While the Britax models install pretty easily (there are still a few tricks to getting them in properly, though), getting the Graco base-and-carrier setup we used when the kids were newborns was pretty nightmarish. My husband claims to have used up his entire vocabulary of swear words as while as making some new ones up while trying to put the thing into our car.

Fortunately, there are a few local resources to help you with this often formidable task. The California Highway Patrol office in Corte Madera offers appointments with its car-seat specialists to make sure your seat is properly installed. Make an appointment by calling (415) 924-1100—and make sure you do it well in advance of when you need to have the seat installed as appointments may need to be made several weeks in advance. But they're free, and they'll usually end up just reinstalling the thing for you if it's in incorrectly. The Novato Police Department offers a similar service (call (415) 899-7017 to make an appointment), as do the Mill Valley and San Anselmo police departments; call them for appointments at (415) 389-4100 ext. 124 and (415) 258-4610, respectively.