New figures from Statistics NZ show child poverty has increased on multiple key measures.
In the year to June, 36,000 more Kiwi children were living below the poverty line, the figures show.
KidsCan said it has more than 200 schools and early childcare centres waiting for support - the longest waitlist since 2018.
Child poverty is measured against nine measures specified in legislation passed in 2018.
In the year to June, two of the three primary measures had a year-on-year increase alongside one of the six supplementary measures.
The number of Kiwi kids in homes experiencing material hardship, a primary measure, increased 2 percent to 12.5 percent compared with the year to June 2022.
Material hardship is defined as a household going without six or more of 17 essential consumption items due to cost.
Items include fresh fruit and vegetables, doctor's visits, good pairs of shoes, car upkeep and the ability to deal with unexpected expenses of $500 or more.
This also increased for groups such as mokopuna Māori (21.5 percent), children with disabilities (22.3 percent) and Pacific children (28.9%).
Children in homes experiencing severe material hardship, a supplementary measure, increased 1.5 percent across the same period - rising to 5.5 percent.
Severe material hardship is when a house goes without nine or more of these essential consumption items due to their cost.
The number of children living in low-income households after housing costs were deducted rose 3 percent to 17.5 percent (one in six children), compared to 14.4 percent in 2022.
However, the number of children living in low-income households before housing costs were deducted saw no statistically significant change and remained at 12.6 percent - or one in eight children.
"For many households, incomes after deducting housing costs did not keep up with inflation," said Abby Johnston, Stats NZ's general manager of social and population insights.
The rate of children in low-income houses after housing costs are deducted is still lower than the baseline year, 2018, when it was at 22.8 percent.
Low-income households are defined as those that have less than 50 percent of the median equivalised disposable household income.
There was no statistically significant difference from the previous year for poverty measures for smaller populations like tamariki Māori, Pacific children and disabled children and they followed the other trends.
However, figures for these groups are harder to measure and, consequently, statistics gathered from them are more uncertain and they generally remain higher than average.
Save the Children has called for the Government to invest in policies that will lift more children and whānau out of poverty following the release of the data.
It highlighted the data fails to include those living in emergency housing, which it calls "the hardest end of poverty".
"Every child and their family need a liveable income that can keep pace with the cost of living," Save the Children New Zealand advocacy director Jacqui Southey said.
Southey is concerned the new Government will worsen existing problems through sanctioning beneficiaries and reducing benefit levels.
UNICEF Aotearoa is also concerned the Government's moves relating to benefits will disproportionately impact on children who are already struggling.
"It is a sad indictment on our society that we still allow children in communities to go without the basics while tax cuts are promised to the wealthy," said Teresa Tepania-Ashton, the director of programmes and advocacy at UNICEF Aotearoa.
"This Government says it is looking to be guided by evidenced-based policy. However, Government indexing benefits to inflation rather than wages flies in the face of evidence that suggests this move could push an additional 13,000 children into poverty.
"How can we justify these decisions?"
Research by UNICEF last year highlighted the crucial role for cash benefits in alleviating poverty amongst children.
KidsCan said the new figures mirror the demand charities are facing.
"We're deeply concerned but sadly not surprised by these figures. The cost-of-living crisis is having a devastating impact on children's lives," said KidsCan chief executive Julie Chapman.
In a recent survey conducted by KidsCan, 65 percent of 347 schools surveyed said poverty was getting worse in their communities.
Only 6 percent said it was improving, while 15 percent said it was static.
