Biodiversity is essential for nature and human well-being. Land use has reduced biodiversity in cities that is associated with altered commensal microbiota and a rising burden of immunological disorders among urban children. The investigators will estimate how rewilding of kindergarten yards affects commensal microbiome, prevalence of allergies, asthma, atopic dermatitis and infections, cortisol levels, cognitive skills and plasma cytokine levels of children. Our specific aims are: To assess if rewilding diversifies health-associated skin, saliva and gut microbiota and reduces infectious diseases and atopic or allergic symptoms. Assess whether the rewilding has positive effects on cognitive skills. Assess whether the rewilding changes cortisol and plasma cytokine levels. The investigators will recruit altogether 320 (160 per treatment) study subjects aged between 1-5 to questionnaire study (Task 2), from which 120 study subjects will be analyzed more detailed using microbiological and blood samples (Task 1).