You have a kid, and you have a car? Stop everything and read this now.

By Marisa Cohen
Updated July 31, 2017
Each product we feature has been independently selected and reviewed by our editorial team. If you make a purchase using the links included, we may earn commission.

Car seats are one of the most important items you’ll ever buy for your child—yet no one seems to have any idea about how to use them properly. (Chrissy Teigen recently admitted to worrying about whether she installed her car seat correctly when she posted this photo of her daughter Luna—and remember when the entire world watched and judged Prince William as he strapped his royal baby into the car for the first time)?

RELATED: 3 Ways to Make Reading More Exciting

We caught up with Ben Hoffman, MD, professor of pediatrics at Oregon Health & Science University and a Certified Child Passenger Safety Technician (CPS) who has been helping parents install car seats safely for two decades, to uncover a few surprising facts parents should know about car seats:

Related Items

Close up of baby in car seat
Credit: Guido Mieth/Getty Images

1 Almost Every New Parent in America Leaves the Entire Contraption Too Loose.

In a study Hoffman published in Pediatrics, he discovered that 95 percent of parents leaving the hospital with their newborn had installed their infant car seat incorrectly—and almost all of those mistakes were pretty significant. “The biggest mistake is leaving the straps too loose—you shouldn’t be able to pinch any slack over the baby’s collarbone,” he explains. “The other big mistake is keeping the chest clip unlocked or too low. It should be up by the baby’s armpits.” Repeat after us: Keep the strap tighter, the clip higher. Also, once the seat is installed, you shouldn’t be able to move the base more than an inch in any direction. Tired, confused, or just a regular mortal? Find a nearby CPS technician to help you out.

2 The Safest Seat Isn't the One You Think It Is.

Instinct would say the center seat in the back of the car is the safest place for the baby—it’s furthest away from any potential impact in an accident. But if you’re using a car seat with lower anchors, most cars only have two positions where the seat can be correctly installed—on either side, next to the door. “In this case, good installation is more important than good location,” says Hoffman.

3 Used Car Seats Are Fine—But Only If You Know Who Used Them.

If you have a car seat left over from an older sibling, cousin, or friend, it’s perfectly fine to pass it down to the next child as long as it hasn’t been damaged or recalled and has all the original parts, saysHoffman. “But you have to be 100 percent sure of the seat’s history, since a seat that’s been in a car accident should never be used again,” he says. That means skipping yard sales and online swaps, unless you really, really trust that the person is telling you everything you need to know about the seat.

4 Like Yogurt and Aspirin, Car Seats Have an Expiration Date.

Of course, if that older cousin passing down his car seat is now in high school, say no thanks. Most seats expire six years from the date of manufacture. You should be able to find the date on a sticker on the seat. “Think of all a car seat goes through—the heat of summer, the cold of winter, getting covered with pee, poop, and Cheerios,” Hoffman explains. “The material goes through degradation over time, and you also want to make sure your car seat has the most up-to-date innovations and safety features.”

5 Unlike Everything Else in Parenting, You Shouldn’t Get Too Excited About Car Seat Milestones.

The rule of thumb is that the seat your kid is in now is safer than the one he’ll be in next (rear-facing has more protection than front-facing; a car seat has more protection than a booster seat; a booster seat has more protection than a seatbelt). This doesn’t mean that you should try to strap your five-foot-tall middle-schooler into an infant seat, but you should keep your kid in his current device until the moment he reaches the weight or height limit, no matter how eager you are for him to reach the next milestone, says Hoffman.

6 You Have to Play Matchmaker Between Your Car and Your Seat.

I’ve been helping parents install car seats for 20 years,and there have been times that no matter what you do, you can’t make a specific seat work in that specific car,” says Hoffman. Sometimes it has to do with the size of the seat, sometimes it has to do with the make of car, sometimes it even has to do with the size of the parent (if Dad is well over six feet tall and has to push the driver’s seat all the way back, there may be less room to maneuver the car seat). “Many retailers will let you take it out of the box and try it in your car before you decide,” Hoffman adds. He also points out that while car seats can range from $50 and $1000, all will meet the same minimum safety requirements, no matter the price.

7 You Should Bring Your Car Seat on an Airplane, Even if You Didn’t Pay for the Baby’s Seat.

“In a perfect world, every baby should be strapped into a car seat while flying in case of turbulence, but it’s not realistic to expect every family to pay full-fare for a seat for a lap baby,” Hoffman says. But here’s a secret many experienced travelers know: If you bring the car seat onto the plane and the flight is not sold out, the attendants will often move you next to an empty seat so you can strap your baby in. If it’s a full flight, you can just gate-check the seat at no extra cost.