That's the view of academics and teachers who have criticised the Education Department for letting inner-city child care centres operate without any outdoor space.

Three Melbourne centres have recently been granted exemptions to national regulations which state that they must provide every child with at least seven square metres of outdoor space.

They have instead created "simulated outdoor environments" – think synthetic grass, murals of forests and clouds, pot plants, sand pits in plastic shells and fake trees made out of concrete pillars.

The move puts children at risk of developing short-sightedness and sets a dangerous precedent, according to University of Melbourne associate professor in early childhood studies Kay Margetts.

She pointed to research which links low levels of natural light with myopia.

"Children need to be outdoors and they need to be able to have opportunities to look into the distance if they want to develop long sightedness," she said.

"Where is the fresh air, where is the sunlight, where is the exposure to seasonal changes?"

As well as benefiting the eyes, experts say outdoor play encourages risk-taking, helps children develop important coordination skills and muscle strength and is a protector against obesity.

Following complaints from teachers, the Australian Education Union met with the department last year to raise concerns about its approval of childcare centres without outdoor space.

"For children to develop in a healthy way physically and mentally they need space to explore and an opportunity to connect with nature," the union's early childhood vice-president Martel Menz said.

"We want to make sure that they aren't cooped up in artificial environments."

The department has signed off on waivers for centres in Highpoint, Collins Street and Melbourne Central where there is limited access to suitable land for childcare services.

Only About Children, which runs a centre on level five of Melbourne Central and has been granted an exemption, has tried to recreate nature with a giant sandpit, a mural of trees, indoor plants and play equipment on artificial grass.

The provider's general manager Peter Warner said this did not negatively impact children's development or learning experience.

Being indoors has a number of perks, and play is never disrupted by Melbourne's extreme weather, he said.

"It's a space that can be used when it is rainy and cold," he said. "In the city, high traffic means that air quality may not be as good. Having the kids in an internal space means we can ensure the best environment for them."

Mr Warner said children were taken on regular outdoor excursions and specialists ensured that kids were hitting their milestones.

Bronwyn Joslyn, a teacher who is on the committee of Environmental Education in Early Childhood, has started a change.org petition which calls on Education Minister James Merlino to ensure children have access to high-quality outdoor play.

"How can it be increasingly acceptable for children to spend their entire child care or kinder day inside?" she said. "Outdoor play makes children resilient and helps them develop a good immune system. It's vital."

When Brigitte Callery and her husband were looking for a kindergarten for their three-year-old daughter Ruby they steered clear of centres with no or limited outdoor space. They settled on one that runs bush kindergarten, where children spend three hours a week learning on the banks of Merri Creek.

"It appealed to me because she will be in nature and exploring, risk-taking and playing different games with her peers in a natural environment."

Early Learning Association Australia chief executive Shane Lucas said it was "not unreasonable" for services to have no outdoor area if they were constrained for space.

But he said they must utilise every opportunity to have recreational space.

"That might involve using verandas. There are a lot of ways of creating a good recreational environment that are not outdoors," he said.

A department spokesman said the exemptions were only granted in exceptional circumstances. He said all the centres with waivers had "light and airy" indoor play equipment and ran regular outdoor excursions.

"Two of the childcare centres are in the CBD, offering parents vital access to childcare where it would otherwise not be available," he said.