Inspectors said services provided by Worcestershire County Council displayed "widespread and serious" failures in provision for both children living in the community, and those who had been taken into care.
Specific problems centre around a failure to recruit "good quality, permanent social workers and managers" and an inconsistent use of thresholds "across the service and at every point of the child's journey".
"Too many children have been left in situations of escalating risk without becoming looked after," the inspection report states.
"Many child protection strategy meetings do not involve all relevant agencies, to allow a thorough discussion of the risks to children.
"As a result, children who require protection from harm and who need urgent improvement in their lives are left in situations of actual and escalating risk of significant harm.
"Children are, however, well supported by the out-of-hours service, where assessments, return home interviews and overall decisions are effective."
Inspectors also said children's views are also not fully considered or acted on and inspectors were also critical that not enough children were seen alone by social workers.
In relation to services for care leavers, inspectors said that they are too often left in inappropriate accommodation and almost half of them are not in employment, education or training.
"Services for care leavers are inadequate, because young people leaving care do not consistently receive the necessary support to make a successful transition to adulthood," the report states.
Council leaders came in for particular criticism for not taking "sufficient action to ensure the protection of vulnerable children".
A safeguarding improvement board set up by the council's chief executive "has not provided sufficient focus to tackle poor practice" and its work has been blighted by "a lack of management oversight", the inspection team's report says.
The report adds that "senior leaders were unaware of the critical issues that were identified by inspectors during the inspection".
However, inspectors did say that, in recent months, a new senior leadership team, including the lead member, director of children's services, independent chair of the Local Safeguarding Children Board (LSCB) and assistant directors for safeguarding and provider services, has taken up post and are starting to provide much-needed focus and drive.
Meanwhile, despite the concerns there was some praise for aspects of adoption services, which were handed a judgment of "requires improvement".
Inspectors found that many children, "including those with complex needs" are successfully adopted through the "tenacity" of the adoption service.
Strong adoption planning and early identification of adopters was welcomed, but more work needs to be done to consider fostering for adoption as an option for children, inspectors added.
The inspection team notes that since the inspection there has been "strong political support" for change "however services remain fragile".
Worcestershire County Council has been contacted for comment.