A well-known pram company has been forced to apologise for a seemingly-innocuous photo of a child in a car seat, but say the blunder has highlighted a common mistake parents make with car seats.

The photo, which appears harmless to the untrained eye, shows a young boy grinning as he sits in a Mountain Buggy car seat, buckled in and wearing a blue jacket.

The picture, which was used in Mountain Buggy’s advertising recently, has prompted complaints as parents point out that children should not be put into car seats wearing jackets, coats, or any bulky type of clothing.

Chief executive of Phil and Teds and Mountain Buggy Campbell Gower told the Herald putting children in the seats with thick clothing on “compromises the integrity of the safety systems underlying that seat”.

Installation of a car seat is the area most parents go wrong, Campbell Gower says. Photo / 123RF

“Obviously if you’ve got a very thick coat which has a lot of padding or whatever in it, then it might make the seatbelt feel tighter than it really is.”

Thick or puffy jackets and coats can then compress under the force of a car crash, meaning the seat belt is now looser on the child.

“The loads in accidents are tremendous,” said Gower, who added their seats were tested with 10,000 newtons, which was equivalent to “having a one-tonne weight hanging off it”.

It was understandable that parents would put their children into the car wearing thick layers, particularly on cold days, but “best practice” was to remove as many layers as was practical before buckling the child in.

Whānau Āwhina Plunket’s principal clinical advisor Karen Magrath said it was “really important” to remove bulky clothing.

“In a car crash, a puffer jacket or any bulky clothing immediately compresses from the force, leaving extra unsafe space between the harness and the child. A child is then not held firmly and securely in the best position in their seat to protect them from injury,” Magrath said.

A Mountain Buggy car seat advertisement has drawn ire online after the child was depicted strapped into the seat with his jacket on.

Mountain Buggy put out an apology for the photo on social media this week, explaining the picture was one sent in by a “beautiful family” and was not taken using models.

Mountain Buggy does not use models for their promotional images, and instead uses pictures given to them by families using their products.

“We acknowledge when we get it wrong,” they said in their statement.

“We made a judgement in error . . . though it is a light jacket overlaying his garment underneath, we understand that we should have either not used it, or ensured that image credits gave the context about the use of the car seat in the image - to eliminate the risk of misinformation on how to install a child in a car seat safely.”

The car was stationary at the time the picture was taken, with the seat rotated outwards for the child to be put in.

“Car seats is a category that requires absolute attention to detail and our team vows to do better; to work on ensuring decisions are made that will promise our safety message not only comes from our copy, but from our imagery.

“We do not want confidence in the integrity of these new seats to be impacted by feelings about this one image, of a child being loaded, wearing a light jacket.”

They said the picture was an “innocent image taken of [the family’s] authentic experience”.

Gower said the biggest mistake parents made was in the way they installed the seats into their cars. He most commonly saw issues with people threading the seatbelt through the base of the car seat incorrectly.

It was also common for parents not to strap their child in tightly enough. The “two-finger test” was a good way to check this - if the harness strap is able to be pinched into a fold vertically with an index finger and thumb, the harness needed to be tightened.

Melissa Nightingale is a Wellington-based reporter who covers crime, justice and news in the capital. She joined the Herald in 2016 and has worked as a journalist for 10 years.