Remember that your Child/ren do not need to be wearing a huge winter jacket in their car seat. For one big reason, it is not met or designed to go under the shoulder straps. Please use a light weight jacket/ a sweater for the shoulder straps to fit properly around your child; keeping them safe. I live in Maine and the winter weather here is crazy, but I do not put a big fluffy jacket on my child like this.
This is my son (Below) in the middle of January 2013 which is correct attire for a car seat for the winter months.