A troubled council has been told young people in its care are at "potential risk" due to pressures on staff.
A letter from Ofsted to the chief executive of Northamptonshire County Council said that social workers were "overwhelmed" and "drowning".
The authority has twice banned itself from spending in 2018, and is being run by government-appointed commissioners.
The government may now appoint an additional commissioner to oversee children's services in the county.
In 2013 the Conservative-controlled county council's children's services was rated inadequate and in 2016 Ofsted inspectors upgraded the rating to "requires improvement".
But Ofsted says standards have "significantly declined" in the last two years and that the service has gone backwards.
They also found that "changes in leadership at corporate and managerial levels [at the county council] have impacted on leaders' ability to respond to identified weaknesses".
'We will put this right'
Ofsted's findings related to a visit carried out by inspectors in October and said children in the county "are not consistently or effectively assessed, supported or protected" when referred to the council's children's social care service.
Inspectors said social work caseloads were "too high" and that "many" social workers were responsible for between 30 and 50 children.
Beyond that, at the time of the visit, 267 children in need of a statutory assessment and social work intervention did not have an allocated social worker, leaving them "at potential risk of harm".
Secretary of State for Housing, Communities and Local Government James Brokenshire said he was "minded" to appoint another commissioner "to stabilise and improve the service so each and every child receives the protection they deserve".
Mr Brokenshire proposed the appointment of former executive commissioner for children's services in Rotherham, Malcolm Newsam.
Cabinet member for children Victoria Perry said "the addition of an individual such as Malcolm Newsam, with all the experience he brings, can only be good news for this county".
"What we must never lose sight of is that if this report means that already children in this county are safer then we must all welcome it and its findings. It is now our duty to fix what has clearly gone wrong."