Urgent action is needed to improve the child support system amid concerns single-parent families are "slipping through the safety net", MPs have warned.
The Work and Pensions Committee said the Child Maintenance Service (CMS) must be tougher on enforcing payment of child support and tackling gaps in its provision for cases of domestic violence.
In a new report, the cross-party group of MPs urged ministers to tackle prolonged under-payment by some absent parents as well as "shameless self-employed" parents who exploit a legal loophole that allows them to avoid paying the right amount of child support to their families.
A high proportion of cases slipped through the cracks when the new system was introduced in 2012, the report also found.
Conservative Heidi Allen, who sits on the committee, said: "We know the balance between state and family is one of the hardest to get right.
"But there is an opportunity to get control of this decades-old issue, by improving the new Child Maintenance Service.
"It is right of course that families sort these issues themselves wherever possible, and the Government only provide a safety net when that doesn't work.
"But a high proportion of ongoing cases from the CSA have not been resolved, they have simply disappeared.
"There must now be a worry that families simply cannot face starting over and are slipping through the safety net."
The report called for greater help for domestic abuse survivors, who it said were being let down by the system which means they have to engage with their abuser over the money owed in child support.
Parents should also be able to challenge unfair child support awards, the committee said, as they called for an end to loopholes for the self-employed.
Ms Allen said: "The victims of this fraud by shameless self-employed parents who play the system, and old-fashioned deadbeat non-payers here, are children.
"The CMS must visibly up its game, to get fair support for parents in the most difficult circumstances, and to send a clear signal that avoiding responsibility for your children is unacceptable.
"The evasion of child support under the guise of ever-changing "self-employment" is also an evasion of tax.
"It is a double hit to the tax payer in the form of lower tax receipts and also benefit payments to parents with care who can't then make ends meet.
"It is therefore essential that the Government reviews this as part of its comprehensive review of self-employment."