Carnival scenes as hundreds march through central London
Hundreds of campaigners calling on the government to end child poverty have joined a march through London.
"Keep the promise" was organised by the Campaign to End Child Poverty, a coalition of 120 organisations.
It says the 2009 Budget is the last real chance the government has to meet its 2010 target to halve child poverty.
After meeting group members, Prime Minister Gordon Brown repeated a pledge to impose a legal duty on government to eradicate child poverty by 2020.
The coalition's report this week said more than a third of UK children live in low-income families or families in poverty.
It found that of the 13,233,320 children in the UK, 5,559,000 are in families that are classed as "struggling".
The End Child Poverty campaign is backed by organisations including Barnardo's, Unicef and the NSPCC.
According to its research, there are 4,634,000 children in England living in low income families, 297,000 in Wales, 428,000 in Scotland and 198,000 in Northern Ireland.
Campaign director Hilary Fisher said: "Poverty has an impact on every aspect of a child's life, health, education and well-being.
"Now is the time for the government to turn their commitment into reality and provide that investment which will make that change."
After a meeting with the group, Mr Brown said he would honour the pledge.
"One of the great causes of this generation is the eradication of child poverty," he said.
"We will, in law, make it the duty of government, by 2020, to have eradicated child poverty in this country."
The government says it has lifted 600,000 children out of poverty since 1999 but a further 2.9 million remain.
Liberal Democrat leader Nick Clegg, who was joining the rally, said the situation was "shameful".
"Everyone in Britain and all political parties have a duty to do everything we can to end child poverty in Britain for good," added Mr Clegg, who wants a simplified benefits system to help families.
Martin Narey, chief executive of Barnardo's and chairman of the campaign, said fulfilling the government's commitments could be Mr Brown's "greatest legacy".
But he said it would take an extra £3bn to meet its 2010 target, less than half of 1% of public expenditure.
CHILD POVERTY: THE NUMBERS
13,233,320 children in the UK
5,559,000 live in low-income families or those in poverty
In 174 of 646 UK constituencies, over 50% of children in poverty
22% of children live in families claiming tax credit
22% of children live in workless families
Worst constituency is Birmingham Ladywood where 81% of children live in or on the brink of poverty
Campaign to End Child Poverty
"The government has made a lot of progress but there are going to be about one million more children in poverty in 2010 than the government promised," he said.
"The prime minister offered his support. We didn't get the promise of the money but we made it very plain to him he must keep his promise."
Hundreds of marchers, including many children, gathered at Millbank, near Lambeth Bridge, before proceeding to Trafalgar Square for a rally with speeches and entertainment.
One Barnardo's worker said: "They need to put money into children's services and then let the professionals do the job with the resources they need."
Another marcher added: "We see two or three generations who are in a cycle of poverty they're not able to get out of."
The official government measure of poverty is where a family is living on below 60% of median household income - the income midway between the highest and lowest.
The Campaign to End Child Poverty defines poverty as when a family has an average of £10 per person per day to live on, or less.