Car seats and winter coats

A bulky winter coat is mostly air. It compresses under load — which is what makes it warm — and in a crash it compresses instantly. The harness was tightened around the coat, so when the coat flattens, the harness is suddenly loose by the thickness of the coat, and the child can move within the restraint at the exact moment they should not.

You do not have to take this on faith. There is a two-minute demonstration you can do in your own car:

1. 01

   Buckle your child in wearing the coat

   Tighten the harness the way you normally would, until it feels snug and you are satisfied with it.

2. 02

   Unbuckle without touching the harness adjuster

   Release the buckle and lift the child out, but do not loosen or adjust the straps at all.

3. 03

   Take the coat off and buckle them back in

   Same harness setting, no coat. Now do the pinch test at the collarbone.

4. 04

   Look at the slack

   In most cases you can gather a substantial fold of webbing — often enough to see daylight between the harness and the child's chest. That gap is what the coat was filling, and it is what would exist in a crash.

None of these require buying anything, which is the main reason this page has no product recommendations on it.

1. 1.Coat on backwards, over the harness. Buckle and tighten the harness against thin clothing, then put the coat on the child backwards like a hospital gown, arms in the sleeves, opening at the back. Warm, and the harness is against the body where it belongs. This is the standard answer and it works from infancy to booster age.
2. 2.A blanket over the top. Buckle and tighten first, then lay a blanket over the harness. Simple, free, and easy for anyone else driving your child to get right.
3. 3.Thin layers underneath. Fleece rather than down. Multiple thin layers are warmer than one thick one anyway and do not compress in the same way.

For infant carriers there is a fourth option: a cover that goes over the outside of the seat with nothing behind the baby's back and nothing between the baby and the harness. Check the seat manufacturer's position, because some make their own and some prohibit third-party covers — and any cover with a layer that sits behind or under the baby is the thing to avoid.

The reason the coat problem matters is that it defeats the one check that catches everything else. After buckling, try to pinch a horizontal fold of harness webbing between your thumb and finger at the child's collarbone. If you can gather a fold, the harness is too loose. If the child is wearing a thick coat, you may pass that test and still have a dangerously loose harness in a crash — which is exactly why the coat comes off first.

Two more cold-weather notes. A car seat left in a freezing car is very cold to sit in, and warming the car for a few minutes is kinder and safer than adding padding. And in cold weather children get out of coats reluctantly, so the backwards-coat habit is worth establishing early with everyone who drives them — it is the sort of thing a grandparent or a babysitter will not know unless told.