Children are being left "at risk of harm" because of the government's failure to develop "credible" plans to improve child protection, MPs warn.
"Urgent" action is needed to end the variations in the quality of help for vulnerable children in England, the Public Accounts Committee says.
The MPs called for the publication of detailed plans to transform child protection services.
The government says it has a relentless focus on keeping children safe.
The MPs said progress had been "too slow" in the five-and-a-half years since a government-commissioned review, the Munro Report, called for a major overhaul of the system.
Professor Eileen Munro was commissioned by then Education Secretary Michael Gove to conduct a review of child protection services.
Her 2011 report called for social workers to be freed from excessive bureaucracy, centrally imposed targets and regulations so that they could spend more time on face-to-face work with families and at-risk youngsters.
Ministers said at the time that they were adopting Prof Munro's principles for the service, but according to the PAC, the government still had "no credible plan to improve services and grow a quality social workforce".
Less than a quarter of services were rated "good" by Ofsted, it said, which the committee described as "by no standards" an improvement.
The PAC called on the DfE to "set out detailed plans, including a timetable and resources, for how it will work with local authorities to transform services".
Ministers needed to explain how they would ensure that all children have equal access to high-quality services, and how they will attract more "high-calibre people" to social work, said the report.
And it called for more resources for Ofsted to conduct quality checks, and greater readiness to intervene to nip local problems in the bud.
Committee chair Meg Hillier said it was "completely unacceptable" that so little progress in the past five years, adding improvements were "woefully overdue".
"Government complacency over improving children's services must end now," said Ms Hillier.
"There are nearly 800,000 children in need of help or protection every year - children who for far too long have been let down by the support available."
The government's target of 2020 to transform the system "better serves Whitehall than it does vulnerable young people in need of help", said Ms Hillier.
She called on the the Department for Education to provide the committee with clear plans to drive improvement.
A DfE spokesman said it had a relentless focus on keeping children safe, and it was wrong to suggest otherwise.
"This year we published plans to deliver excellent children's social care across the country, and through new legislation are further strengthening protection for the most vulnerable children and transforming the support available to them.
"We take tough action where councils are failing children, stepping in to make sure improvement plans are taken forward as a matter of urgency."
He added that councils had increased spending on children's social care by around £850m since 2010-11, to nearly £7bn last year.
It added that the Children and Social Work Bill, currently going through Parliament, would strengthen protections for vulnerable children and improve support for looked after and formerly looked after children in schools.
And local authorities would be enabled to develop new and better ways of delivering children's services through the innovation programme.
But the Local Government Association said children's services were handling 65% more initial contacts in recent years - up from 1.2m in 2007 to 2m in 2013-14.
Councillor Richard Watts, chairman of the LGA's Children and Young People Board, said: "The number of children on child protection plans has increased by more than 60% during the same period.
"But local authorities have faced significant funding reductions over this same period, and with such a big rise in demand for services, it's vital that local authorities have the resources they need to keep children and young people safe."
"Child protection reform and improvement support have been largely removed from local government in recent years and increasingly centralised within Whitehall instead," he added.