Winter car seat safety is on many parents' minds this time of year.

That's because many of us have heard the warning: Putting your kids in puffy winter coats into their car seats could put them in grave danger.

It’s an easy mistake to make. You’re running out the door in icy temperatures and you throw a chunky winter coat on your child before jumping into the car. But what’s cozy for kids as they play outdoors isn’t necessarily the safest when buckling up.

Sue Auriemma from Kids and Cars showed TODAY why: When a child is wearing a winter coat, it may feel like they are strapped snugly into a car seat when the straps are actually dangerously loose.

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At an official crash test lab in Michigan, a child dummy that appeared to be securely strapped into a car seat came hurtling out of it in a simulated 30-mph crash.

But what coats are car seat-friendly? Are car-seat ponchos better?

This test showed the dangers of wearing a bulky coat, which endangers car-seat safety. Parents should choose car seat-friendly coat options. TODAY

Bulky winter coats can pose a serious threat when worn under the straps of car seats and even booster seats, by creating too much space in between your child’s body and the harness itself.

“Anything between the child and the straps is compressible; it’s like having space, which creates more risk that the child could thrust forward into the straps in the event of a crash," said Dr. Benjamin Hoffman, medical director of the Tom Sargent Safety Center at Doernbecher Children's Hospital in Portland, Oregon.

Dr. Hoffman said that the first rule of thumb when you buckle your child up is that you don’t want them wearing anything more than what they’d be wearing indoors, such as a sweatshirt or a sweater.

"Instead of putting the coat on him, you can put the coat over him to keep him warm," Auriemma said. "Or you can use a blanket."

RELATED: After daughter sustains major injuries, mom warns about proper car seat use

Dr. Hoffman said that when teaching technicians how to safely install car seats, they use a fairly straightforward trick. With your thumb and your index finger, pinch the harness near the child’s collar bone. If you are unable to pinch any excess webbing when you pinch the strap, the harness is considered snug enough. This is called the pinch test and it is one of the top five things to keep in mind when you do a car seat checkup, according to Safe Kids Worldwide.

“If it’s an older child, take their jacket and put their arms through it backwards over the harness," said Dr. Hoffman. "If the child is younger, tuck a blanket around the straps. There are some items that aren’t manufactured by the car seats to keep a child warm, but we don’t recommend using anything that alters the way a child interacts with a car seat. The bottom line is that nothing should come between a child and the car seat straps.”

This doesn’t just apply to young infants; children in booster seats should follow the same rules.

Taking the time to remove your child’s coat before buckling up might feel like a hassle if you’re running out the door, but this extra step can make a serious impact.

“I can see why this approach could be considered difficult,” said Dr. Hoffman. “But remember, most crashes occur within 6 miles of home at relatively slow speed. But even at 30 mph, the force on a 10-pound infant is more than a 10-pound bowling ball falling from a 3 story window. Take the time — I’ve seen what can happen in the event of a crash.”

The advice even applies to adults: Experts say they shouldn't wear their winter coats when they're behind the wheel or riding in a car.

With reporting by Morgan Brasfield.

This article was originally published on Dec. 14, 2015.