"There's never been a comprehensive study done like this," said the project's principal investigator, Associate Professor Louise Signal of Otago University.
Health researchers have grown increasingly concerned at child obesity rates.
Professor Signal said research suggested junk food promotion had an influence on children equal to that from parents and peers.
A review of scientific literature had also found promotional activity was affecting children's preferences, purchasing and consumption.
"Children tell us that they do see a lot of advertising, but we've never quantified it across the entire range of media."
Where it had been looked at, researchers had found a considerable amount of junk food advertising.
Her colleagues had drawn the same conclusion after a recent survey of Facebook and social media.
Professor Signal and a team of researchers last year conducted a pilot project in the Wellington area, using six intermediate-school children.
Wearing lenses smaller than that of an iPhone and able to be hung on a lanyard or attached to a lapel, the children went about their day as the cameras filmed images every 10 seconds.
Professor Signal said the initial findings prompted researchers to widen the project to include 224 children in Wellington from next year.
Each young volunteer would wear the cameras over a weekend and on two weekdays, and could use a privacy function to switch the cameras off when they needed to.
Part of a $5 million Health Research Council programme directed by the University of Auckland, the study will produce millions of images to be analysed using a computer algorithm.
Findings would be published within two years.
"It will enable us to describe what food advertising they see - and also quantify the extent and nature of it," Professor Signal said.
"As a parent myself, I'm very interested because parents aren't with their older children all of the time, they don't necessarily know where they go, and a lot of it slides under the radar anyway."
A report by the Restaurant Association and the Auckland University of Technology this year revealed Kiwis ate $1.5 billion worth of takeaways last year - more than 9 per cent above the previous 12 months.
That equates to about $330 - enough for 63 Big Macs - for every man, woman and child in the country.
The Government is working on a national strategy on obesity reduction, which is expected to be released within a few months.
The Food and Grocery Council's chief executive, Katherine Rich, is sceptical about the study.
"A child might see an ad on a bus shelter, but that doesn't mean that child is going to act on that image and eat themselves into a frenzy," she said.
"It might be an interesting study - let's see what the research says - but it would be quite dangerous to assume that seeing an image is the same as acting on that image."
Franchises were restricted by national regulations, including the Children's Food Classification System, and most had policies on marketing to children.
Coca-Cola's prohibited "direct targeting of children under 12 in any media for any brand messaging" and meant the company could not promote its products in schools or to children at company-sponsored sampling events.
