Severe Government budget cuts pose a "real danger" of pushing more families into poverty, ministers have been warned.
In a joint report, the UK's four Children's Commissioners said they were "deeply concerned" that failure to properly assess the impact of funding reductions at all levels of government would leave some youngsters facing "disproportionate hardship".
They have called for an urgent review of how the coalition's spending cuts will affect vulnerable families and for "vital" children's services to be protected.
The commissioners, who promote the interests of children and young people, raise serious concerns about the "high levels of persistent poverty" across the UK.
Around 3.8 million children - one in three - are living in relative poverty, the report found.
Although the group acknowledges "tough decisions may be required" to revive Britain's ailing economy, they fear "those most vulnerable in society" are being hit hardest.
Speaking on behalf of the four commissioners, Keith Towler, who holds the post in Wales, said: "We, as independent children's champions, have a duty to hold UK Government and its devolved administrations to account.
"We are in constant dialogue with our respective governments to ensure the rights, needs and best interests of every child are upheld."
A spokesman for the Department for Education said: "The UK State Party is committed to promoting children's rights and to the implementation of the United Nations Convention on the Rights of the Child. This year we celebrate the 20th anniversary of our ratification of the UNCRC.
"The report from the four Children's Commissioners is a timely reminder of how much we have done to implement the UNCRC, and where we still need to make progress. We are determined to deliver our obligations towards the UNCRC to make children's rights a reality across the State Party."
© 2011 Press Association