Updated May 12, 2013.

Experts often warn that parents use car seats incorrectly, making common car seat mistakes such as either using the wrong seat, putting it in the wrong position in the car, using the wrong harness slots, or putting the harness clip in the wrong position.

During the winter, when many kids wear extra clothing, including sweaters and heavy winter coats, these extra layers can pose another 'hidden hazard' as you try to use your child's car seat correctly.

Winter Coats and Car Seats

One of the basics of correct car seat installation, in addition to buckling the car seat tightly into your vehicle, is that your child is 'buckled snugly' into the car seat itself. If the harness straps are loose, then your child can be injured or could even fly out of the car seat if you are in a crash.
Remember that the American Academy of Pediatrics advises that "It's OK to adjust the straps to allow for thicker clothes, but make sure the harness still holds the child snugly. Also, remember to tighten the straps again after the thicker clothes are no longer needed."

Keep in mind that this will likely not apply to very thick and heavy winter coats though, which may become compressed under the harness straps in a crash, become too loose, and may allow your child to become injured or even ejected from the seat and/or car.

Instead of putting your child in a car seat with a heavy winter coat, the Texas Department of Public Safety recommends that you 'keep your child in the clothes they will be wearing when they are indoors.

Place the child in the infant seat or car seat, making sure the harness straps are snug over the shoulders and that they lie straight and flat down to the buckle. Buckle the child in and THEN put the coat or blanket OVER them -- on TOP of the harness system. You can even turn the coat around and put his arms through the sleeves after he is buckled into his car seat. This will ensure your kids are kept snug in their seat, the harness system is able to do its job in the event of a crash, and that the kids stay warm.'

The National Highway Traffic Safety Administration also recommends that 'to keep your baby the safest, always remove bulky clothing or blankets before you place the child in the seat. Then, put the blanket or coat over the baby. You should never place anything thick underneath the baby, unless that item came with the car seat originally — which tells you it's been tested by the manufacturer. When a child is wearing a thick coat, it's hard to tell if you have a good harness fit, which is crucial. A coat can add a lot of slack, reducing the level of protection for your child in a crash.'

<sub>Sources:

American Academy of Pediatrics. Car Safety Seats: A Guide for Families.

Fast Facts from the Texas Department of Public Safety. Child Safety Seats: Winter Safety.

National Highway Traffic Safety Administration Frequently Asked Questions.</sub>