Local authority social services in England that are found to be failing vulnerable children will face tough new measures, the PM is to announce.
Under the plans, departments judged inadequate by Ofsted will have six months to improve or be taken over by high-performing councils and charities.
Commissioners will be sent to run three authorities immediately.
“We, the state, are their parents; and we are failing them,” David Cameron will say of society’s most vulnerable.
“It is our duty to put this right,” he will add.
Experts will be sent in to run Sunderland City Council’s unit immediately, after inspectors from the care watchdog Ofsted found “serious and widespread” failings.
One child was hurt by her father and a second drowned in the bath after concerns were not properly dealt with, serious case reviews found. Sunderland said it did not “shy away from the criticisms”.
Commissioners will go into Norfolk and Sandwell children’s services immediately too, with a view to taking them over within a year.
Councils’ failings have been exposed by a series of recent child abuse cases in Rochdale, Rotherham, Derby and Oxfordshire.
Education Secretary Nicky Morgan told the BBC there will be “much less tolerance of failure”.
“Ofsted will go in and inspect more quickly, particularly if there are reports either of inadequacies in the way that the department is being run or we obviously receive intelligence from whistleblowers,” she said.
Where councils do not make significant improvements within six months of their Ofsted inspection, there will be similar measures to those used to deal with failing schools.
A new service leader, a commissioner, will be put in place.
Mrs Morgan said: “If necessary they will appoint a trust, which is a not-for-profit organisation, which could be run by something like a community interest company or a charity to run the services to make sure they get back up to the level that the vulnerable children who rely on the protection of these services deserve.”
High-performing councils, including Hampshire, Leeds and Durham, child protection experts and charities will be asked to form the trusts to take over the worst children’s services and will have powers to get rid of staff.
Like academy schools, such councils will be given greater freedom to make changes.
More than £100m is to be spent attracting high-calibre graduates into social work and new trust sponsors from the charity sector will be recruited to help deliver children’s services.
“This will be one of the big landmark reforms of this Parliament, as transformative as what we did in education in the last,” Mr Cameron will say later, at an event in south London.
“And it shows how serious we are about confronting state failure and tackling some of the biggest social problems in our country.”
NSPCC chief executive Peter Wanless welcomed the changes, saying too frequently services had failed to protect children.
“When this happens, swift action is an absolute priority to prevent tragedies that shame us all,” he said.
“And we need to ensure that if tragedy does befall a child, that we then learn the lessons from serious case reviews, something that year after year is not done.”
Barnardo’s chief executive Javed Khan said: “There must be options, where it is best for the child, to use the expertise of the voluntary sector to complement those already in place.
“We want to work with local authorities and others in local communities to ensure the best outcomes for children.”