Denmark trended on social media this week when a Tiktok post, later also shared on Twitter, showed a series of videos of Danish strollers or prams parked outside on streets.

A number of the clips in the video show empty strollers parked outside kindergartens, but others presumably do indeed have sleeping babies in them.

This should not come as a surprise, given it’s common practice in Denmark to put babies and toddlers down for their naps outdoors, usually in their strollers.

Some social media commenters expressed shock at the video, with a fair few calling it bad parenting.

This is so interesting! Imagine just leaving your kid outside to nap while you go about your business, unbothered. Wow. pic.twitter.com/Ehqg32Mjoj

— Alma (@AlmaChronicle) September 27, 2022

This week’s Tiktok and Twitter posts are not the first time Danish babies napping outside has caught international attention.

Back in 2013, newspaper Jyllands-Posten reported that the “BBC is surprised that Scandinavian children sleep outside” in response to an article by the British broadcaster titled “The babies who nap in sub-zero temperatures”.

“The Scandinavian custom of letting infants sleep outside is causing a stir,” the paper wrote.

Research cited in both the British and Danish articles suggests that there may be benefits to letting children sleep outdoors.

That includes a study from Oulo University in Finland based on a survey of parents.

“Babies clearly slept longer outdoors than indoors,” lead researcher Marjo Tourula told the BBC. Indoor naps lasted between one and two hours while outdoor naps lasted from 1.5 to three hours, the survey found.

“Probably the restriction of movements by clothing could increase the length of sleep, and a cold environment makes swaddling possible without overheating,” Tourula said.

Swedish paediatrician Margareta Blennow told the BBC that the Swedish Environmental Protection Agency had found conflicting results.

“In some studies they found pre-schoolers who spent many hours outside generally – not just for naps – took fewer days off than those who spent most of their time indoors,” she said, adding “in other studies there wasn’t a difference”.

District nurse and author Helen Lyng Hansen told newspaper Ekstra Bladet in 2013 that babies sleeping outside “is a tradition we have in Denmark.”

“It’s part of our culture that we have an idea that it is good for children to sleep outside and get fresh, red cheeks. But there’s no evidence to say that it makes children healthier,” she said.

A page on district nursing advice website Sundhedsplejerkse.dk says that “there are not yet any scientific studies that can prove that sleeping outdoors makes a difference. But the experiences of parents and experts suggests that children seem to sleep well outside.”

All experts stress that it is important for babies and small children to be appropriately dressed for sleeping outside.

Newborn infants are not put outside to sleep, with most parents waiting until around five to six weeks of age, particularly in colder seasons. Health service advice says infants weighing under 3 kilograms should sleep indoors. Children who have a fever or are otherwise sick should also not sleep outside, according to general advice.

Temperatures below minus 10 degrees Celsius or very misty conditions are not suitable for outside sleeping and naps outside should not last more than around 2 hours.

In Denmark, the standard outfit for children sleeping outside in winter is a woollen sovedragt or full-length suit on top of up to three layers of their regular clothes or pyjamas. They will also wear gloves, a scarf and an elefanthue or non-face-covering balaclava.

A design of blanket from the brand Voksi, referred to as a Voksi pose (“Voksi bag”) is the most popular choice for outdoors sleeping. The blanket can be folded and fastened to enclose the baby and has a hood-shaped part at the top.

The child is usually then placed under an outer blanket or rug and inside the stroller, which has rain covers pulled over if needed.

These layers are gradually reduced during the warmer seasons.

Although images of prams parked on streets are perhaps the most striking feature of the practice, this is not where most Danish babies sleep. Gardens, balconies and kindergartens are far more common places for parents or carers to put young children down for a nap.

That’s not to say a little one sleeping in a pram outside a café or similar public place isn’t unheard of. When this happens, the parent will be sat somewhere in view or use a baby alarm.

That parents nevertheless feel comfortable leaving children to sleep on the street can seem unbelievable to those witnessing the practice for the first time.

“There’s also something about us living in safe Denmark,” retired district nurse and author Sigrid Riise told Ekstra Bladet in 2013.

“We have always dared to leave our children outside, even though we have begun to keep an eye on them more in recent years,” she said.