The government has stepped in at a London council after it was revealed some children are being left at risk of "significant harm".
It comes after Croydon Council was criticised in a report by regulator Ofsted for "widespread and serious failures" in children's services.
The Department for Education has appointed a commissioner for children's services to oversee improvements.
The council said "immediate action" had been taken to improve performance.
The report said "weak managerial oversight at all levels" at the council has meant basic social work practice is not of a good enough standard.
Foster carers said they felt "poorly supported" by the council, and Ofsted found the council's fostering service was "not in compliance with regulations".
The council is also taking too long to place children into care, leaving them at risk of "significant harm" from neglectful parenting, the report said.
It also noted people leaving care in Croydon were not being consistently prepared for independent living, and were not being made aware of their entitlements.
The council was last rated in 2012 as adequate.
Commissioner Eleanor Brazil will work with the council to improve the service.
She was previously brought into Haringey Council in the aftermath of the Baby P scandal.
Councillor Alisa Flemming, cabinet member for children, young people and learning, said: "The care and safety of vulnerable children and young people is an absolute priority for this council.
"I will do whatever it takes to make sure that we are providing them with the high-quality services that they deserve."