Yard size does not affect children's physical activity levels, according to a new study, suggesting outdoor play mightn't be impacted as cities densify and backyards shrink.

The research led by the Murdoch Children's Research Institute (MCRI) and the University of Melbourne, showed no association between yard space and greenness and physical activity, highlighting a child's capacity to engage in outdoor play regardless of the size or amount of vegetation in their yards.   

MCRI researcher Jessica Oakley said prior to this study few had examined the relationship between the outdoor home environment and child physical activity despite concerns that decreasing yard sizes and high-rise apartment living could come at cost to health.

The research, published in  BMC Public Health, involved 5276 six-year-olds living in Melbourne. Physical activity was recorded using an accelerometer, a wearable tool that measures acceleration, over eight days.

The research found for every 10 per cent increase in yard size there was almost no rise in sedentary behaviour and light or moderate to vigorous physical activity. On average the children were meeting the physical activity guidelines of at least 60 minutes a day of moderate to vigorous physical activity.

Ms Oakley said the findings showed yard size and greenness didn't have a major impact on children's physical activity.

"This suggests that child physical activity may not suffer as we densify our cities and reduce the size of yards," she said. "There was also no link between the amount of yard greenness and physical activity or outdoor play."

MCRI's and the University of Melbourne's Dr Suzanne Mavoa said with outdoor play in younger children decreasing, identifying ways to promote physical activity was a public health priority.

"Physical activity has health and developmental benefits for young children, including mitigating the risks of obesity and chronic diseases such as diabetes and heart disease and improving motor and cognitive development," she said.  

"As cities become increasingly densified, urban design, shared indoor and outdoor spaces and schools will need to play a greater role in supporting young children's physical activity and active play."

MCRI Professor and GenV Scientific Director Melissa Wake said it was also crucial that State Governments and local councils also protected public green spaces for families with no access to yards.

"This research indicates the importance and value of public outdoor spaces such as parks in supporting physical activity and play for all children, no matter their background or where they live," she said. "Improving equity in health outcomes for all children is a core value of MCRI's GenV research project.

"GenV – Generation Victoria - is one of the world's largest-ever birth and parent cohort studies. It will help government and policy-makers assess and access future research studies similar to this one to help better plan for policy solutions now and into the future, including looking at the environments children are growing up in."

Researchers from Deakin University also contributed to the study.

Publication: Jessica Oakley, Rachel L. Peters, Melissa Wake, Anneke C. Grobler, Jessica A. Kerr, Kate Lycett, Raisa Cassim, Melissa Russell, Cong Sun, Mimi L.K. Tang, Jennifer J. Koplin, Suzanne Mavoa. 'Backyard Benefits? A cross-sectional study of yard size and greenness and children's physical activity and outdoor play.' BMC Public Health. DOI: 10.1186/s12889-021-11475-4

*The content of this communication is the sole responsibility of MCRI and does not reflect the views of the NHMRC.

Available for interview:                      

Jessica Oakley, MCRI researcher

Dr Suzanne Mavoa, Senior Research Fellow, MCRI and the University of Melbourne
Professor Melissa Wake, MCRI Group Leader, Prevention Innovation and Scientific Director, Gen V
Media Contact:

Bridie Byrne

MCRI communications specialist

+61 457 365 848

About MCRI

The Murdoch Children's Research Institute (MCRI) is the largest child health research institute in Australia committed to making discoveries and developing treatments to improve child and adolescent health in Australia and around the world. They are pioneering new treatments, trialling better vaccines and improving ways of diagnosing and helping sick babies, children and adolescents. It is one of the only research institutes in Australia to offer genetic testing to find answers for families of children with previously undiagnosed conditions.


SM, RLP, and KL are supported by National Health and Medical Research Council Early Career Fellowships (#1121035, #1160779, #1091124 respectively). The HealthNuts study is supported by the National Health and Medical Research Council, Ilhan Food Allergy Foundation, AnaphylaxiStop, the Charles and Sylvia Viertel Medical Research Foundation and the Victorian Government's Operational Infrastructure Support Program.