A major report into spending on children's services has called for the Assembly government to set out its funding plans in regular budget statements.
The cross-party children and young people committee said a lack of transparency makes it impossible to see how much cash is reaching front- line services and how effectively it is being spent.
It also wants children to become more "budget-literate" and for school councils to play a bigger part in the budget-setting process.
The inquiry, which took place earlier this year, heard evidence from government officials, academics, children's organisations and young people. The committee makes 11 proposals for the Assembly government in the report, published this month.
The Assembly government has made tentative steps to trial a national children's budgeting exercise - Wales is the first UK nation to do so - but the report says the information is not sufficiently accurate to provide a clear picture.
Helen Mary Jones, the committee's chairwoman, said cash must be spent strategically to promote the rights and well-being of children and young people.
"We need to know what the long-term objectives of such expenditure are and we need to have informed discussions about whether such expenditure is adequate for the task," she said.
"We believe a greater public understanding of Wales' budgetary decisions and their impacts will ultimately lead to better decisions."
The idea of a children's budget, setting out national and local spending, was proposed by the charity Save the Children. It believes this would give the public a clearer view of the Government's spending priorities.
Giving evidence to the committee, David Reynolds, professor of education at Plymouth University, said statements detailing local government spending on children would be very valuable because of huge differences across the country.
Since he made those comments, new figures have been released revealing that the gap in per-pupil funding between the highest and lowest-spending authorities has grown to a record high.
The report says the Government should publish a single strategy detailing outcomes it expects from its expenditure on children, and that it should set similar goals with local authorities.
It wants comprehensive budget statements published at national and local level at least every three years to identify clearly how much cash has been spent both directly and indirectly on children and young people.
Children should also become involved in funding issues at local level and through school councils, it says, citing good practice in France, where pupils, parents, teachers and employees in each school debate projects they deem to be priorities.
The report urges schools to teach budget literacy, supported by web-based materials created by the Government.
Witnesses, including Save the Children, Professor Reynolds and the Welsh Local Government Association, all suggested that financial education could take place within the personal, health and social education curriculum.