A child development expert is urging parents to monitor their children's screen time.

A survey has revealed two-thirds of Kiwi kids have their own cellphone by the age of 11.

Nathan Wallis told Mike Hosking two hours of device free time each day can reduce chances of children and teenagers experiencing anxiety or depression.

"But it is difficult at that age to regulate your own behaviour, so I think it's got to come back to us as parents to help them with that, or modelling that and having device free time ourselves."

LISTEN ABOVE