The Children's Commissioner for Wales says he thinks a target to cut child poverty in half by 2010 was a "red herring" and "unrealistic".
Youngsters in poverty are missing out on 'occasions,' says the report
Keith Towler said the UK and assembly governments should explain now how they planned to end child poverty by 2020.
The Social Justice Minister admitted the rate of progress in Wales had slowed down over the last two years.
But Dr Brian Gibbons AM said the issue continued to be tackled and "had to be a top priority".
Mr Towler, who took over as children's commissioner last week, told BBC Wales: "I'm beginning to think actually that the 2010 target is a bit of red herrring. The absolute commitment was to end child poverty by 2020.
"What we need the Westminster government and the Welsh Assembly Government [to do is] to come back to us now and say how are we going to achieve that by 2020. We can't fail children by 2020."
He made his comments after the publication of a new report, which said 90,000 children in Wales were missing out on the likes of holidays and school trips.
Save the Children wants more take-up of benefits and tax credit encouraged.
The charity, along with the Bevan Foundation think-tank, said Wales' poorest children are missing out on significant occasions rather than physical items.
It found 90,000 children - or 13% - live in households which could be classed as in "severe poverty".
They go without two or more goods or services because their families cannot afford them.
The things that they are more commonly denied are "occasions" such as school trips, holidays or inviting friends round for tea.
The two organisations are calling on the assembly government to increase benefit and tax credit take-up, put appropriate support programmes in place and make public services deliver for families facing multiple disadvantages.
They are also calling for the assembly government to establish its own child poverty policy unit to take them forward.
Dr Gibbons welcomed the report and told BBC Radio Wales that while the rate of progess against child poverty in Wales had slowed down over last two years it was still below that of England.
He denied a lack of "joined-up thinking" and said the assembly government was in the process of establishing an expert group on child poverty.
"The fact that we've reduced child poverty more quickly here in Wales than the rest of the United Kingdom suggested that it isn't the case.
"There is no doubt that in the measures used something of the order of 28% of children in Wales are in poverty is totally unacceptable and that has got to be a top priority of the Welsh Assembly Government."