Children's services are at a "tipping point", with record numbers of youngsters now in care, town hall bosses have warned.
The equivalent of 90 youngsters a day are entering the care system, according to the Local Government Association, which urged government to plug a funding gap to help councils support vulnerable children.
The LGA, which represents local authorities in England and Wales, said councils needed more cash to ensure families got the right support they needed and avoided children being placed in care if possible.
Government figures show there were 72,670 "looked after children" in England as of the end of March, up 3% on the year before. These are youngsters who are in the care of the local authority, such as those in foster care or waiting to be adopted.
In addition, 32,810 youngsters - equivalent to 90 a day - entered the care system, and started to be looked after. This figure is up 2% on 2016.
Richard Watts, chair of the LGA's children and young people board, said: "Children's services are at a tipping point with growing demand for support combining with ongoing council funding pressures to become unsustainable.
"Last year saw the biggest rise in the number of children in care for seven years.
"With 90 children coming into care every day, our calls for urgent funding to support these children and invest in children and their families are becoming increasingly urgent.
"Children's services face a £2 billion funding gap by 2020.
"If nothing is done to address this funding gap, crucial services that many children and families across the country desperately rely on will be put at risk.
"We are calling on the Government to use the Autumn Budget to commit to fully funding children's services and invest in improving services to ensure vulnerable children get the appropriate support and protection they need."
Anne Longfield, Children's Commissioner for England, said: "With a rising population of children in care at a time when council funding faces enormous cuts, the pressures on local authorities are intense.
"Councils tell me they are stretching every sinew to meet their responsibilities to children who are highly vulnerable. Many though are having to do so at the cost of reducing services that prevent family crises.
"I hope the Treasury will recognise that it makes economic and social sense to invest in families before crisis hits."
Children's Minister Robert Goodwill said: "Councils will receive more than £200 billion for local services, including children's social care, up to 2020. This is part of a historic four-year settlement which means councils can plan ahead with certainty.
"All children deserve the best possible support and while some councils are doing excellent work, we want to help ensure more local authorities provide good and outstanding services.
"That's why we have invested £200 million through our Children's Social Care Innovation Programme, providing councils and the voluntary and community sector with funding and support to develop new and better ways of delivering services for vulnerable children and families.
"As well as this I am also announcing up to £20m to support further improvement in children's social care services."
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