Over the past year, studies have shown that babies and toddlers should not wear heavy, puffy coats or buntings in their car seats.
The reason is that the bulkiness of the coat adds about four inches to the length of the strap on the seat, and tests conducted have shown that baby is more likely to be dislodged from the seat during a crash than without lengthening the straps to accommodate a coat. A study from the University of Michigan showed in a crash test that the dummy child wearing a puffy winter coat was much more likely to be thrown from the seat on impact.
Luckily, you can still keep your child warm and safe in the colder months. Dress your baby in layers if you’re going on a car trip. Put him in a long-sleeved onesie with fleece pants, socks and shoes. Then, layer a fleece jacket over his onesie and strap him into his car seat. Use a heavy blanket or quilted car seat cover to put OVER the baby and the straps, so nothing is obstructing the safe and correct use of the car seat straps. Baby will be snuggly for the ride.