Play was defined as an unstructured activity outside of school, such as backyard cricket.
More than one in three children said they had no one to play with, one third said they ran out of ideas for play, and parents said children struggled to amuse themselves without electronic devices.
Professor Grant Schofield, director of AUT University's Centre for Physical Activity and Nutrition, wrote in a foreword to the report that the findings were "astonishing".
"[Children] need to 'unplug' and venture into the backyard to let their imagination run wild. Let them take some risks. Let them make mistakes. This is how they will learn."
He told the Herald that an over-reliance on structured activities such as sports training or ballet was part of the problem.
Research in Britain showed today's parents spent more time with their kids, but much of that was spent getting to and from organised activities.
Professor Schofield, who has three primary school-aged children, said the same situation applied here.
"It's mostly sitting in cars ... if you drive half an hour somewhere, do half an hour's activity, then drive half an hour back," he said.
"It's just as easy to open the back door, kick them outside, then start chucking a few cricket balls around."
He said other studies showed unstructured play was critical to developing the prefrontal cortex, a part of the brain that helps people to understand risk and control impulsivity and emotion.
"It's better to learn about risk and consequences and controlling your emotion when you're 8 and up a tree, than when you're 18 behind the wheel of a Subaru, getting chased by the cops."
Almost all adults surveyed in the study said they believed play was essential to a child's development.
Yesterday Megan Paki watched as her boys Lucien, 7, and Raphael Perez, 4, made the most of a children's playground despite the drizzly conditions.
She said it could be a struggle to enforce the right balance between time spent playing and time spent using technology.
"It's not just the TV. It's the phone ... it's computers at home as well.
"The way technology is moving, that's quite a big shift there. So you do have to be a bit more careful," she said.
STATE OF PLAY
* 46 per cent of children aged 8 to 12 not playing every day.
* Sedentary and structured activities such as sports training blamed.
* Unstructured play key to healthy brain development.