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1 July 2015 Last updated at 06:46 BST
Sally Holland said children needed to be protected from the impact of Westminster austerity measures.
She said too many children in Wales were being denied a decent childhood.
Ms Holland and the commissioners for England, Scotland and Northern Ireland said in a report to the United Nations they were alarmed at how welfare changes had increased child poverty.
They said under current policies figures were expected to rise, with 4.7m children projected to be living in poverty by 2020.
Figures released last week showed a third of children in Wales lived in poverty - defined as such when in a household with an income below 60% of the UK average of Â£453 a week.
The charity Barnardo's welcomed the report, and said millions of children were being failed.

Four people were on board the Irish Coastguard Rescue Helicopter 116 when it went down on 14 March.
Cpt Dara Fitzpatrick died after she was rescued from the sea.
Police said that the body of another crew member had been found but they could not yet confirm identification.
The missing coastguard crew were Cpt Mark Duffy, winch operator Paul Ormsby and winchman Ciaran Smith - it is not yet known which member has been found.
Search teams are trying to remove the body of the crew member from the cockpit of the aircraft, but investigators said sea conditions have meant dives to the wreckage on Saturday have been prevented.
On Friday the black box recorder from the rescue helicopter was recovered.
The chief inspector with the Irish Air Accident Investigation Unit (IAAIU) Jurgen Whyte said: "We're happy to announce we had a positive recovery of the data recorder at 1630 from the seabed just off Blackrock."
Mr Whyte said the recorder will be brought to Dublin before being sent to the UK air accident investigation branch where it will be prepared for download, hopefully successfully, by Tuesday or Wednesday of next week.
Late on Friday afternoon, searchers began diving at Blackrock island off the coast of Blacksod, County Mayo, where the wreckage of the helicopter was found on Wednesday
It was discovered about 60m west of Blackrock island, in waters about 40m deep.
R116 lost contact with the Irish Coastguard at about 01:00 on 14 March, as it made its final approach to Blacksod refuelling depot.
The crew had been providing communications support to another coastguard helicopter that had been deployed to take an injured fisherman to hospital.
The wreckage of R116 was pinpointed after search teams deployed a remotely-operated vehicle (ROV), fitted with an underwater camera.

The A43 Corby relief road has been open for 12 months and has seen daily traffic levels rise from 8,000 to 11,300 since it opened last May.
But many lorries and cars are still taking the old road through Geddington.
Michael Clarke, from the county council highways department, said: "Old habits die hard and some sat-navs have still not been updated for the new route".
He is pleased more vehicles are now choosing to use the new road, which was expected to carry 25,000 vehicles a day.
Poor signage has also been blamed for the lack of cars.
"It's developing just like the M1 when it opened. It had little traffic at first but is now well used," Mr Clarke said.
"When the penny drops and drivers use the road they realise how quick it is."
He said the road formed part of plans for new roads which bypass the villages of Flore and Weedon near Daventry.
Mark Rowley, chair of Geddington Parish Council, said the road is making some difference to congestion in the village.
He wants the county council to do more to persuade local transport companies to use the new relief road.
Andrew Howard, managing director of a logistics firm at King's Cliffe, said his drivers were encouraged to use the road from the day it opened.
"It is faster and less stressful for our drivers. We made them aware of its advantages straight away," he said.
"It's a faster route to customers in the north of England."
The UK government must stop making cuts to benefits or more children will be "pushed into poverty", the children's commissioner for Wales has said.
[NEXT_CONCEPT]
The body of a crew member has been located in the wreckage of a rescue helicopter which crashed earlier this month, gardaÃ­ (Irish police) have confirmed.
[NEXT_CONCEPT]
Out of date sat-navs have been blamed for motorists' slow uptake of a new £35m road in Northamptonshire.