Thick winter coats or snowsuits can keep your baby warm but they can compromise your child's car seat safety. In order for car seats and boosters to function properly, the straps need to remain tight against the child's chest. Winter coats and snowsuits change the way a child fits into the car seat.

When the car seat straps don't fit the child properly, there is a chance they will move more than they should during an accident. Their heads and other body parts will be more likely to hit hard parts of the car (like the seat in front, window, or doorframe), which causes an increased risk of injury.

Coat Compression Is Dangerous

The car seat harness needs to stay close to the child's body at all times. All coats and clothing will compress in a crash, but thicker winter coats and snowsuits could compress enough to create a lot of slack in the harness. The effect could be as though you never tightened the harness straps at all. Those loose straps may not be able to keep baby in the car seat, or in the car at all.﻿﻿

Keep Your Child Warm and Safe

Even if you can't safely use your child's winter coat in the car seat, there are ways to keep baby warm when temperatures drop.﻿﻿

Dress your baby or toddler in thin layers of clothing. Each layer holds warm air. The layer next to the skin should be close-fitting, such as tights, leggings, long underwear, or a long-sleeved bodysuit.

Cover this with pants and a shirt or sweater. Some polar fleece jackets and snowsuits are thin and snug-fitting enough to be used in a car seat (Sherpa fleece is too bulky). Dress your child in a hat, mittens, and warm socks or booties to keep head, hands, and feet warm. These won't interfere with the snugness of the straps.

Warm-up your vehicle before you go. If you can, keep the carrier portion of your infant seat indoors so it isn't cold when you put your child into it. Take off any coat that is too thick or bulky before buckling the car seat. If your child is wearing a coat that you know is unsafe for the car seat (you can determine that using the chalk test described below), take it off.

Buckle the seat, adjusting the straps each time you do. You should only be able to get one finger under the harness at your child's collarbone. If you can pinch the strap, it is too loose.

Add a blanket on top. Once your child is safely buckled into the seat, you can cover them with a light blanket tucked around the sides. Or you can put the child's coat on backward over their arms to keep them warm without compromising safety. If needed, you can add another heavier blanket over the top of the infant seat. As the car heats up, you can remove a blanket so your child doesn't overheat.

Finally, make sure nothing is behind the child's back. No portion of the blanket or car seat cover should be behind your child's back.

Check Winter Coats for Car Seat Safety This test can show you that a coat or snowsuit might compress too much in a crash and why it is safer to use thin layers and a blanket over the car seat instead. It's not recommended that parents uninstall a convertible seat to make changes. When you're ready to try the test, bring your child out to the car. If you're still using a portable infant seat, these can safely and easily be brought into the house for the test. Make sure your child is dressed in their winter coat or snowsuit. Put the child in the car seat and buckle the harnesses as you normally would before car travel, making sure they are tight enough to fit your child appropriately. Using chalk, mark the tail of the car seat strap where it comes out from the car seat. (See a video of this chalk test.) Take the child out of the car seat. Take the coat off your child. Put the child back in the car seat and buckle the harnesses again. Adjust the strap so that the chalk line is where it was when the coat was on. If you can fit more than one finger under the harness at the child's collarbone, the coat is too thick and is not safe for use with the car seat. (See what properly snug straps look like.)

Check Car Seat Covers for Safety

Many companies offer thick car seat covers that act like a bunting for babies in the winter. Parents should avoid using any aftermarket cover, blanket, sleeping bag, or bunting where any part of the product has to go in before the baby is buckled snug.

If the entire product can go on after the baby is safely buckled, it is not interfering with the function of the car seat in a crash. Often the packaging of these covers states that the product meets all federal car seat safety guidelines. However, there are no federal guidelines governing after-market accessories.

These extra car seat covers and buntings could interfere with the function of the car seat harness, and many car seat manufacturers will void your car seat warranty if after-market accessories are used.

From a crash perspective, a cover or accessory is safe to use if it can be put on in its entirety after your baby is buckled snug. This test ensures that the product is not interfering with the snugness or position of the harness straps on the baby's body.

Winter car seat covers that fit over the top of the car seat like a shower cap can usually be used safely. These should not have a layer under the child. Be sure the child's face is not covered (these covers usually have a hole over the baby's face).