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You're not supposed to put a winter jacket under car seat straps - so I guess I just let my baby freeze while the car warms up? I get why, but it's very impractical and frustrating in Canada. — D.

Packing our kids into bulky jackets and snowsuits like Ralphie's little brother in A Christmas Story is a necessary ritual of Canadian winter, but puffy winter gear can stop a car seat from doing its job.

"In a crash the harness holds your child in place to prevent injuries," says Katherine Hutka, president of the Child Passenger Safety Association of Canada.

"Even when the straps are tight, if you add a layer of bulky padding between the child and the car seat straps, this padding can compress in the force of the crash, making the straps suddenly too loose and putting your child at risk of injuries or ejection."

Think of rolling up a sleeping bag so it will fit in that little bag it came with — as you push down, the air gets pushed out and the filling gets flattened.

When that happens to a child's jacket or a baby's bunting bag, the straps are no longer tight enough to keep them safe.

When a car going 50 km/h hits something, the weight of people and objects in the car are multiplied by 20, says the Société de l'assurance automobile du Quebec (SAAQ), the provincial insurer. An 18-kg child becomes a 360-kg projectile.

If there's anything thick between straps and your child — like winter clothes, a blanket or an aftermarket pad for the straps — the seat stops working like it was designed, and crash-tested, to.

Consumer Reports magazine says one way to tell if winter clothes are too bulky for a seat is to put your child in the seat with the jacket on and tighten the straps. Then, take your child out of the seat, but leave the straps as they are.

Put your child back in, this time without the jacket (this might have to be done inside the house if it's December). If the strap is loose enough that you can can pinch the slack between your thumb and forefinger, then the coat is too bulky.

Heavy winter gear can also change a child's position in the car seat, so the straps might not sit properly on their shoulders or kid's might be sitting taller than they actually are. That's an issue for older children in booster seats too, Hutka says.

"A booster seat boosts a child up so that the seat belt fits across the strongest bones — the lap belt should fit low on the pelvis," Hutka says. "If you add a snowsuit or bulky coat underneath the belt, the lap belt will ride up onto the child's soft abdomen and puts him or her at risk of severe injuries in a crash."

Transport Canada and the provinces don't ban kids from wearing heavy winter gear in car seats, but they don't recommend it.

"When using winter clothes, always ensure that the harness system is tight, compressing the material to ensure a snug fit," says Transport Canada spokesperson Natasha Gauthier in an email. "Read your car seat user guide or contact the manufacturer for more information."

So how do you protect your kid from freezing and from getting hurt in a crash? Put them in thinner, warm layers instead of one bulky jacket or snowsuit, Hutka says.

"Families can dress their babies and children in layers to keep them warm and safe — fleece is a good top layer for trapping heat without adding padding under the harness or seat belt," Hutka says. "Wear hats, mitts and boots with a fleece jacket in the car seat or booster seat."

Once kids are buckled in, blankets are okay — as long as they're over the straps.

"When it's really cold, kids can wear their puffy coats over top of these layers on the way to the car," Hutka says. "After they are safely buckled, they can wear their coat backwards over their arms to stay warm."

Once the car warms up, kids can kick off the blankets so they don't get too hot, Hutka says. "Parents can pull over to remove the blankets for younger babies who are most at risk of overheating in the car," she says.

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