Very interesting results from a scientific study carried out in Finland looking at how the immune system in children improved only after a month when being given the chance to work with plants and soil. (Reported via Science Alert October 2020 https://www.sciencealert.com/daycares-in-finland-built-a-backyard-forest-and-it-changed-children-s-immune-systems on the study coordinated by the Natural Resources Institute Finland (Luke) https://www.helsinki.fi/en/news/life-science-news/a-forest-based-yard-improved-the-immune-system-of-daycare-children-in-only-a-month)
Previous studies had shown that children living in urban lifestyles through lack of contact with nature had reduced diversity of gut microbes which in turn increase the risk of disorders of the immune system. Other additional studies had found that children living in rural areas in contact with nature had lower probability of catching an illness from an immune system disorder.
In this study the outside play areas of urban daycare centres were planted out with grass turf, planters and plants of the forest undergrowth. Children were also allowed to plant and tend crops.
After just a month of playing 5 times a week with nature, the researchers found the 75 children aged 3-5 years had increased microbial diversity in the skin and also changes in blood counts.
“Increases in gammaproteobacteria, which strengthen the skin’s immune defence, increased the content of the multifunctional TGF-β1-cytokine in blood and reduced the content of interleukin-17A, which is connected to immune-transmitted diseases”Natural Resources Institute Finland (Luke) (2020) 
Children in the study who had access to these nature yards had similar intestinal microbiota of children who visited the forest every day.
The authors also stated this low cost access to nature through creating green areas would improve children’s motor skills, ability to concentrate as well as a closer relationship to nature.
 Natural Resources Institute Finland (Luke) (2020) ‘A forest-based yard improved the immune system of daycare children in only a month‘ University of Helsinki, https://www.helsinki.fi/en/news/life-science-news/a-forest-based-yard-improved-the-immune-system-of-daycare-children-in-only-a-month (accessed 26/10/2020)