Good Egg Safety, which gives advice on car seat safety, issued the video to demonstrate how loose car seat straps can be when a child is wearing a winter coat.
"In a collision, the harness isn’t as close to your child’s body as it needs to be to allow it to properly restrain them," the woman presenting the video said.
In the video a girl has her straps tightly fastened while wearing a puffy jacket, however when her jacket is taken off, the straps are shown to be dangerously loose.
Kevin Clinton, head of road safety at the Royal Society for the Prevention of Accidents (RoSPA), told HuffPost UK Parents: "Thick clothing can prevent a child car seat harness fitting the child properly.
"Parents should check this on every journey; if more than two fingers can fit between the child's chest and the harness, it is too loose."
If you are worried about your children being cold, Good Egg Child Safety said there are plenty of ways to keep them warm in the car without a coat on.
On the website, it states: "For babies, use a cosy toes (foot muff) approved by the child seat manufacturer, or fold a thin blanket in half and tuck it tightly around your baby over the harness, once they are strapped in correctly.
"Make sure any blankets do not come up higher than armpit level.
"For children, strap them into their car seat properly then tuck a blanket around them. Your child will be able to remove the blanket if they get too hot, which they cannot do when they have their coat on, this can lead to them overheating."
This isn't the first time this issue has been raised by parents.
In October 2014, a dad's Facebook post which showed photos of how loose a child's straps can be when wearing a coat went viral.
He wrote: "Thick winter coats and car seats do not mix! In a crash, the winter coat will become compressed and allow your child to be ejected from the car seat through the obvious slack in the restraints.
"Try warming up your car before hand, or just putting the coat over them as a blanket, after you have buckled them in. #keepallthebabiessafe."
The post has had more than 120,000 shares.