The UK Government aims to halve child poverty by 2010
Nearly 68,000 children in Wales live in poverty despite having at least one parent in work, says new research.
Researcher the Institute for Public Policy Research (IPPR) wants the UK Government to improve the minimum wage and tax credits for poorer families.
The UK Government said it was committed to meeting its target of halving child poverty by 2010.
The Welsh Assembly Government said tackling child poverty was key to "a socially just and prosperous Wales".
The IPPR said 600,000 children across the UK had been lifted out of poverty in the past 10 years.
But the total number of poor children in working households had stayed the same at 1.4m, it added.
WHO IS POOR?
Household income less than 60% of median for similar households
Single adult with no children - net income less than £108 per week after income tax and housing costs
Couple with no children - net income less than £186pw after income tax and housing costs
Couple with two children - net income less than £301pw after income tax and housing costs
Lone parent with two children - net income less than £223pw after income tax and housing costs
Source: Joseph Rowntree Foundation
Graeme Cooke of the IPPR said the international definition of poverty was household income at less than 60% of median incomes.
For a couple with one child under 11, that meant living on less than £260 a week. He said a quarter of childre in the UK under that level.
A spokesman for the Treasury said reforms to tax and benefits since 1997 had "greatly improved" work incentives and made work pay.
"The Government is committed to meeting its target of halving child poverty by 2010, and decisions on tax credits and financial support will be taken in the budget and pre-budget report in the usual way," he added.
The improvements to tax credits and the national minimum wage suggested by the IPPR report are the responsibility of the UK Government.
A Welsh Assembly Government spokesman said it was tackling child poverty by improving income levels for families and children in poverty from UK Government sources, promoting financial well-being and improving the life chances of children and families in poverty.
"However, we recognise that we must work alongside our partners in the UK as many levers, particularly around income poverty, are not devolved," he said.
The assembly government said the abolition of child poverty was "a key requirement in achieving a socially just and economically prosperous Wales".
It said it was committed to the aim in the One Wales agreement which led to the coalition government between Labour and Plaid Cymru in Cardiff Bay.