Most winter coats are filled with bulky insulation ⏤ that’s what makes them warm. Unfortunately, that same insulation creates space between a child’s chest and the car seat strap, which should fit snuggly when tightened. It’s actually something of an illusion for parents. When the harness is secure, a child wearing a big coat feels just as tight in the seat as they would if they were wearing a t-shirt. Even the popular pinch test ⏤ in which you check for excess slack in the harness by pinching it with your thumb and forefinger ⏤ works. It feels correctly secured. But it’s not even close to being tight enough. In fact, according to experts at the Car Seat Lady, an organization dedicated to child safety, a standard puffy coat adds four inches of slack to a car-seat harness. That’s the difference, they cleverly point out, between a pair of pants with a 34-inch waist and one with a 38-incher. Huge difference, as anybody who’s ever lost some weight knows. That excess slack not only allows the harnesses to easily slide off the child’s shoulders in an accident but also puts the child at risk of being thrown clean out of the seat altogether. The Today Show ran some crash test dummies to demonstrate a few years back, and the results were dramatic. The coat remained in the seat; the child did not.

How to Tell If Your Kid’s Coat Is Too Big for Their Car Seat

So then, how big is too big when it comes to your kid’s coat? And what about that fleece jacket — does it count? There’s an easy way to find out. Dress your child in their coat or jacket, zip them up, and safely secure them in the car seat as if you didn’t know you were making a potentially fatal mistake. Make sure the shoulder straps are tight. Don’t drive anywhere. Instead, unfasten the straps without loosening them ⏤ not even a hair ⏤ and remove the child from the seat. Take the coat off and return the kid to the car seat. Clip them in but don’t tighten it. How much slack do you have in the shoulder straps? If the child still fits securely ⏤ chest clip at armpit level, straps snug to the body, no slack can be pinched ⏤ the coat is fine. You’re in the clear. More likely than not, however, you’re mind will be blown by the amount of excess space the coat was occupying.

How to Keep Kids Warm in a Car Seat Without a Coat

Now that you’re not putting your infant, toddler, or kid of any size into a car seat wearing a coat, you still have to keep them warm. It’s your parental duty. And it’s still 10 degrees out. In addition to dressing them in layers, you essentially have two old-school options, and one new, depending on the size of the baby:

Cover them with blankets. You should always have an extra blanket in the car in the winter anyway, in case of an emergency breakdown. But the key benefit to layering the child with multiple blankets is that you can remove each as the vehicle warms up. That way, you keep the child from overheating. The number of blankets you use depends on how cold it is and how long the drive is.Cover them with their coat. They can either use their coat like a blanket, or, if they’re older and want to be cool, they can wear it backward.Cover them with an attachable car seat cover. This is the ideal choice for newborns and infants since it won’t bulk up around the face. Just make sure that it fits over the car seat and in no way attaches through the shoulder harnesses.Find a car-seat approved winter coat. Buckle Me is a line of coats that are designed specifically to be worn in car seats — as well as during the day-to-day. The coat’s opening has been moved from the middle of the coat to the side, essentially turning the entire front into a door. Once unfastened, the front panel can be pulled back so the car seat’s shoulder harnesses can be secured directly over the child’s chest as you normally would, with no extra padding in the way.