Children of all ages are at risk of not doing enough exercise, researchers have warned.

A review of more than 50 studies, covering a total of 22,000 young people, found all children are at risk from a decline in physical activity.

The decrease in exercise fell steadily from the age of four or five in both boys and girls around the world.

The study, led by the University of Strathclyde, counters a widely-held view that physical activity does not decline until adolescence and is chiefly among girls.

Researchers say the benefits of active need to be promoted to children and their parents even before they start school.

Statistics published this week show almost a quarter – 22% – of primary one pupils in Scotland are at risk of being overweight or obese.

The ISD report warned there are now “substantial inequalities in child unhealthy weight across Scotland”, with the problem worsening for children in the poorest areas.

Professor John Reilly, of Strathclyde’s school of psychological sciences & health, said: “Higher levels of what is defined as moderate to vigorous physical activity in children improve their bone health, brain development and learning, levels of body fatness, cardiovascular and metabolic health and sleep.

“However, despite these many important benefits, only a minority of children and adolescents meet recommended levels of physical activity.

“The view that physical activity is high in children and does not decline until adolescence – and even then chiefly among girls – continues to be widely held among policymakers and practitioners around the world.

“As a result, policies and practices aimed at promoting activity have focused on adolescent girls, who are seen as a group at high risk group of low and declining physical activity; our study indicates that, while the relative decline is greater among girls, there is no one high risk group.

“All children face a high risk and physical activity needs to be promoted to them – and their parents – before they even start school.”

The research, published in the journal Obesity Reviews, assessed studies of activity levels in children and young people aged between two and 18, covering Australia, New Zealand, the US, Mexico and many countries in Europe, including the UK.

Daily activity fell by three to four minutes each year overall, although it remained higher at weekends and on holidays.

Previous Strathclyde-led research about children in the north-east of England found that physical activity levels could start tailing off as early as the age of seven.

Professor Reilly added: “While we found a lack of studies covering developing countries, our findings do appear to bear out the conclusions of previous research and suggest that this is a worldwide problem.”

The study also involved researchers from University College London, the University of Glasgow and the Aspetar Orthopaedic and Sports Medicine Hospital in Doha, Qatar.