Relating to my post a couple of weeks ago, here is a good test to determine if your child's coat, sweater or sweatshirt is safe to use in the carseat.
Take the car seat into the house.
Put the winter coat or snowsuit on the child.
Put the child in the car seat and buckle the harnesses as you normally would before car travel. Adjust the straps to the appropriate fit for your child.
Take the child out of the car seat without loosening the straps at all.
Take the coat off your child.
Put the child back in the car seat and buckle the harnesses again, but do not tighten the straps.
If you can fit more than two fingers under the harness at the child's shoulder bone, the coat is too thick and is not safe for use with the car seat.