Wales has become the first UK nation to provide a definitive breakdown of how much public money is spent on children - and where.
But an education expert told TES Cymru this week that the figures were unreliable. David Reynolds, professor of education at Plymouth University, said the figures were skewed because they were calculated too simplistically.
"It is clear that you can allocate the direct benefits of public expenditure for children - so the schools budget, for example, goes to children," he said. "It's the indirect stuff that is more difficult to determine."
The official estimates, released by the Assembly government last week, revealed that around 28 per cent of government spending (pound;4.4 billion) went directly on children. There was also a breakdown of education expenditure.
But Professor Reynolds cited cancer spending as one area where the amount spent on children had simply been extrapolated from what was spent on the entire population. "Generally, younger people don't get cancer as much as older people, so where's the sense in that?" he said.
The figures were produced in response to a major inquiry into child budgeting by the Assembly's Children and Young People committee.
Eleri Thomas, programme director for Save the Children in Wales, welcomed the figures, saying that the charity had been calling for them for the past four years. The organisation was one of several to give evidence to the committee lamenting a lack of government accountability over child budgeting.
Ms Thomas said: "We were encouraged by the level of transparency and hope that this will happen on a regular basis. By doing this, we can monitor how much is spent on children over time and compare it with other countries."
She said it would help if future budgets were made clearer to a wider audience: "It's incredibly valuable for the public, including children and young people, to be aware of budgeting."
But Dr Phil Dixon, director of ATL Cymru, suggested changes were needed to the way school funds are allocated - a view shared in the past by other unions.
"The bulk of school funding should come via a developed and comprehensive needs-based formula rather than one simply based on pupil numbers," he said.
Last year, research undertaken by Professor Reynolds for TES Cymru revealed that education spending in Wales has been 6.4 per cent less than the UK average since devolution.
The United Nations Convention on the Rights of the Child, which the Assembly government adopted in 2004, requires national spending on children to be transparent.
An Assembly government spokesman said it would be impractical to work out whether children benefited more than other age groups in some areas. But he added that spending on children would form part of the government's work plan for 2009-10.