Health researchers say the high cost of nutritious food is damaging children's education and wellbeing.
A study led by the University of Auckland found the cost of a nutritious diet had risen by 35 percent between 2018 and 2023, and was far out of reach for the majority of low-income families.
Lead author Dr Joanna Strom tracked the weekly price of a nutritious diet for a family of four.
"We modelled a few different 'food baskets' for children of different ages, and overall this low-cost healthy food basket has gone up about 35 percent from 2018 to 2023, and more so over the last two years," she said.
The average weekly cost for a basket to feed two parents, a 7-year-old girl, and a 14-year-old boy had risen from $230 in 2018 to $309 in 2023.
Most of that increase was in 2022 and 2023, rising 25 percent in just two years.
Strom said she decided to do the study after witnessing the effects of food insecurity first-hand.
"I was motivated by some of my work as a GP where I've seen the negative effects of food insecurity and poor nutrition," she said.
"Plus I'm a mum with three growing kids, so I see my grocery bill going up."
Nutrition was a particular concern for low-income families or those on the benefit.
"It's really tricky if you've got a lower income," Strom said.
"We also modelled this looking at some research the Child Poverty Action Group had done, and one of the things we showed was that if a family on a benefit with two kids was to purchase these foods, they would actually be going backwards over $200 a week."
She said she could not blame parents for choosing to buy larger quantities of junk food over smaller portions of fruits and vegetables.
"At the end of the day, we don't want children with hungry tummies," she said
"A lot of junk food is cheaper, and so that is a concern. We need to keep doing more to try and make healthy choices easier choices, and I think that involves looking at costs across the whole system."
But she emphasised the negative impact poor nutrition could have on children.
"As [kids] grow and develop, food not only is important for their learning, very hard to concentrate if you have a hungry tummy, but also there's lots of links with food and mental health as well as physical development as well," she said.
"These things don't happen in isolation, we need to keep looking at the whole picture of things, the whole system. We want people to live active lives, to be able to exercise and move their bodies and eat well."
Strom urged the government to take definitive steps to reduce food insecurity.
"I would like to see work across the system, and that includes thinking about income support, housing costs, and then through into the food system thinking about how we're producing food, where that food is going, how and where it's being sold, as well as supporting different community initiatives."