A quarter of all preschool children have "developmental difficulties" in their health, behaviour and learning according to a new study.
Consultant developmental paediatrician at Starship Hospital and lead researcher Dr Jin Russell said the results show a strong link between poverty and child development.
She said she knew from the work she did with children on the ground that poverty had an impact on their development.
But, to find out that about one in four Kiwi children weren't reaching their full developmental potential "really took me by surprise", she said of the data.
The study of more than 6000 children aged between 4 to 5 measured four areas of development: physical health, motor skills, emotional and behavioural development, and communication and learning.
The authors found that 19.5% of the children studied had problems in their early learning skills.
"They had more difficulty identifying letters, so early literacy skills... and their ability to concentrate, focus and switch tasks," Russell said.
Just under 6% had "more physical health problems than other children, more chronic conditions".
One group in the study also recorded low scores "in multiple developmental domains".
Russell said that while this was the smallest group, at only 3.7%, these children will "be significantly behind their peers".
"Both in their ability to speak and communicate, understand emotional cues, to regulate their behaviour and also to apply themselves to their learning."
The study also showed children from disadvantaged backgrounds were between one and a half to two times as likely to fall into the study's "suboptimal" categories.
"A key finding was that socioeconomic disadvantage from before the child was born has a predictive effect, an influence, on a child's development," she said.
But while the numbers paint a grim picture for the economically disadvantaged, Māori and Pasifika children were also 30 to 45% more likely to fall behind.
"And that was independent of their socio-economic position," Russell said.
She said the results highlight the need to "substantially strengthen" The Well Child Tamariki Ora Programme, which a 2021 review found was outdated and inequitable and failed to meet the needs of Māori children.
"We need to ensure this programme works for every child so they can reach their potential."
This is even more critical said Russell, when you consider the study's data was collected in 2013, seven years before the detrimental impacts of school closures and the isolation of lockdown.
"We are parenting the pandemic generation, we have a lot of hardship in the country right now.
"So we need to pay attention to these results."