As temperatures drop, many parents could be making a potentially fatal mistake by putting their kids in winter coats while they are in car seats.

When a child is wearing a winter coat, it may feel like they are strapped into the car seat, but the harness straps are dangerously loose against the squishy coat.

Kinzie Evrard, a child safety seat expert with Norton Children’s Prevention and Wellness, said the coat keeps the child from being restrained in the event of a crash.

Check if your child’s coat is too big and bulky to wear under their car seat harness

• Put the coat on your child; sit the child in the car seat and fasten the harness. Tighten the harness at the child’s shoulders until you can no longer pinch any of the harness webbing with your thumb and forefinger.
• Without loosening the harness, remove your child from the seat.
• Remove the coat; put your child back in the seat and buckle the harness straps, which are still adjusted as they were with the coat.
• If you can now pinch the webbing between your thumb and forefinger, then the coat is too bulky to be worn under the harness.