Children with absent parents will have a chunk of their maintenance creamed off by the Government when the Child Support Agency is replaced.
Four per cent of all payments made through the new system will be kept back to cover costs.
The poorest children will lose out under the coalition’s reforms.
Tory Work and Pensions Secretary Iain Duncan Smith says the changes, which include a £20 fee just to lodge a claim, are an incentive for estranged couples to come to an amicable private deal without the state’s help.
But campaigners say that is not a realistic option where absent parents – usually fathers – try to avoid taking responsibility for their offspring.