His comments come in the wake of a British government briefing document showing children who spend too much time in front of the television or playing computer games have less confidence, are more anxious, and develop depression.
Mr Markwick said one school of thought suggested many modern day children did not have basic movement skills, which made them less confident to play sport.
Although there were numerous reasons for this, he suggested schools were less likely to prioritise physical activity.
Wellington clinical psychologist Josephine Leech, who specialises in child and family issues, said children who spent more time inside and in front of television were more likely to have problems and were not exposed to life's challenges.
"I think [the UK briefing] is consistent with other research about television watching and the effects on children," she said.
"These things are quite well known, that sedentary children who are not out exercising, not out mixing socially, are more likely to have problems, less likely to have concentration spans that allow them to succeed at school and less likely to have exposure to both successes and failures that life throws up and [to] develop a more resilient temperament as a result."
The British study, titled How Healthy Behaviour Supports Children's Wellbeing, was published last week by Public Health England.
- additional reporting
George Driver
