Official figures on the number of children living in poverty in the UK are expected to be revised down over concerns they have not been accurately reflecting household income.
For more than 30 years, poverty statistics have been based on an annual survey of households across the UK.
But officials believe those taking part in the survey have been under-reporting how much they receive in benefits.
From next month, child poverty estimates will use data from benefit records, which is likely to mean figures dating back to 2018 will be lower than previously stated.
The Department of Work and Pensions insists improving the accuracy of its statistics will not change its commitment to tackling poverty.
Prime Minister Sir Keir Starmer has said reducing child poverty by the next election in 2029 is one of his government's top priorities.
Labour's long-awaited child poverty reduction strategy, launched at the end of last year, is based on figures showing it had reached a record high of 4.5 million children.
It is not known by how much this figure will change when the new counting system kicks in from March.
But the Resolution Foundation think tank told the BBC it was likely that "the UK's child poverty rate in recent years will be revised down" as a result of the new approach.
The think tank has estimated that the number of children in relative poverty could have been about 500,000 lower in 2016-17 than official figures showed.
The revision is not expected to have a big impact on government projections that its policies could lift 500,000 children out of relative poverty by 2030.
Action for Children, which campaigns to end child poverty, welcomed any improvement to how poverty data is collected and interpreted.
"But whichever way it is measured, hardship among families with children has been getting worse in recent years," Lucy Schonegevel, the charity's director of influencing, told the BBC
She said while "better data will give us a clearer picture, it must ultimately lead to better outcomes for children".
But there is a big gap between what people told the household survey they were receiving in benefits and what the government actually paid out.
In 2023, households reported £190bn in benefits and so-called administrative data on welfare payments totalled £243bn, a gap of £44bn.
A person is deemed by the government to be in relative poverty if they are living in households with income below 60% of the median in a given year.
Median income is the exact midpoint of a population's income distribution, where 50% of people or households earn more than that amount, and 50% earn less.
Official figures for the number and rate of people in relative and absolute poverty are calculated using data from the Family Resources Survey (FRS).
The survey gathers information from more than 19,000 households in the UK annually and the findings are weighted to produce estimates for the whole population.
The DWP has access to a range of administrative datasets covering benefits payments, HMRC tax records and payslips.
A data protection law passed in 2018 allows the DWP to link these records to survey responses, meaning the department can produce more accurate figures for household incomes.
The amount households receive in benefits and the number of claimants are not changing as a result of this revision.
The DWP believes benefits income is under-reported because of respondent misreporting, which is a common problem for surveys.
The under-accounting of benefits income in the FRS has been broadly stable over the years and those in government believe conclusions drawn from the survey data are still valid.
But Resolution Foundation research has suggested that falls in child poverty in the 2000s - when Labour was last in government - were bigger than government statistics suggested at the time.
The think tank believes with corrected data, the government led by Tony Blair may have hit the high-profile child poverty target it missed in 2004-05.
Sir Keir's government has not set an explicit numerical target for reducing child poverty, beyond stating that it wants it to fall.
Lifting the two-child benefit cap is estimated to mean 450,000 fewer children will be in poverty by 2029-30.
But in analysis of the government's child poverty strategy, the Institute for Fiscal Studies said there was "considerable uncertainty over how large a reduction in measured poverty these policies will ultimately deliver", partly because of concerns over survey data.
Tom Wernham, senior research economist at the Institute for Fiscal Studies, told the BBC using administrative records to "correct benefit amounts is going to be a big improvement to the quality of the data underpinning the UK's official income and poverty statistics, and we definitely welcome that".
"This is especially important given the Scottish government and now UK government are targeting measures of child poverty based on this data, and benefits are a key source of income for this group," Wernham said.
The Centre for Social Justice (CSJ) think tank said it expects the new survey will show there were fewer people in relative low income than previously thought.
"Many of the children the government claims will move out of poverty live in households who were just below the relative low-income line," said Benjamin Gregg, the head of welfare research at the think tank.
"The forthcoming changes to the FRS will likely show many of these children were already not in relative low-income."
Gregg said the revision "shows the shortcomings of relying on income-based measures of poverty".
He said the CSJ preferred the material deprivation statistic, which measures whether people lack what are commonly held to be necessities.
A report by the think tank found that a child growing up in a workless household was four times more likely to be materially deprived than in a working household.
"The government should ensure that it targets policies and resources towards tackling the root causes of poverty, rather than relying on flawed relative income measures," Gregg said.
A DWP spokesperson said: "Every child deserves the best start in life and by scrapping the two-child limit as part of our child poverty strategy we will lift 550,000 children out of poverty by the end of this parliament.
"We're also working to drive down living costs and prevent families from falling into poverty in the first place, increasing the national living wage, cutting an average £150 from household energy bills and creating a genuine safety net for households through the £1bn multi-year Crisis and Resilience fund."