Ministers have insisted they were trying to be "more ambitious" about tackling child poverty with controversial plans to change the way it is measured.
Liberal Democrat Schools Minister David Laws, appearing alongside Conservative Work and Pensions Secretary Iain Duncan Smith, denied that their proposals were about "massaging the figures".
They want to move away from the previous Labour governments' focus on relative household income as an indicator of child poverty and use a "multidimensional" measure which takes into account factors like worklessness, family stability and parents' health and skills.
But the move has led to concern among some campaigners that the coalition is trying to duck commitments to abolishing child poverty by 2020.
Launching a consultation on the plans at Clyde Children's Centre in Deptford, south east London, Mr Duncan Smith acknowledged that money "matters" but insisted it was not "absolutely representative of a child's life chances".
"A fixation on the element of relative income or driving people over an arbitrary line does little to identify those entrenched in disadvantage or to transform their lives," he said.
The new measure would provide a much better indication of how many children are in poverty and to what degree," he said.
"It must be robust in showing the total number of children living in poverty in the UK and the severity of the problem."
Mr Laws said income would "always be at the heart of what it means to be poor". "We are not going to run away from that basic truth," he said. But other factors need to be taken into consideration as well, he said.
"Child poverty in the UK is way too high. It's at unacceptable levels and it has been for too long. This consultation is about being more ambitious as a country, not being less ambitious." Mr Laws added: "It's not about abandoning the past and massaging the figures."