Putting a toddler in a car seat seems like a no-brainer, right? But you may be making a mistake that could potentially be fatal for that precious little one.

We have a couple of grandchildren who use car seats, and it wasn't that long ago we had a couple of little ones, and I had no idea that winter clothing can greatly reduce the effectiveness of kids' car seats.

NBC News visited an official crash test lab in Michigan, and learned that bulky winter coats can actually allow children to slip out of car seats during a crash. In the video below, you'll see just how much slack is left between car seat straps and the kids they're supposed to protect, when kids are wearing warm winter coats.

Experts advise parents and grandparents to put the kids in car seats in just their street clothes, and use a blanket or the child's coat to cover them in order to keep warm.

Stay safe!