East Sussex County Council has delivered the warning as the council considers council-wide funding reductions, including cuts to programmes aimed at avoiding care proceedings and keeping families together.
Between 2019/20 and 2021/22 a total of £3.65m cuts are proposed across children's services, which is led by Stuart Gallimore, the current president of the Association of Directors of Children's Services (ADCS).
This includes £854,000 worth of reductions to safeguarding services, including training and programmes that social workers can access that target vulnerable families and ensure problems do not escalate.
Under the plans family group conferences will be stopped, as will an outreach service for 16- to 24-year-olds at risk of exploitation.
A "problem-solving team" that supports the Family Drug and Alcohol Court will also cease. This court is an alternative way of dealing with care proceedings where drugs and alcohol are an issue, by offering support that aims to keep families together.
In addition, there will be a reduction of assessments for families going through court proceedings and funding for the Foundations Project, which works with families where a child has already been take into care.
"The impact of these reductions is likely to mean that more children may become subject to child protection plans or enter or stay longer in the care system," states a document being presented to councillors ahead of a cabinet meeting on 13 November.
It adds: "Though not statutory, these services are an important contributor to preventing children requiring a child protection plan or being taken into care."
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The proposed children's services cuts also include £1m worth of reductions to early help services, which will result in fewer vulnerable families being supported.
This is "likely to result in working with fewer families and focusing our support to those families most at risk of social care intervention and the problems that are most likely to lead to crisis (mental health, substance misuse and domestic violence)", adds the council document.
The proposals to cut family group conferencing in East Sussex comes days after the Department for Education announced that is handing Leeds council £4.85m to put in place measures including an expansion of a family group conference service.
In August Gallimore warned that unless the government provides extra funding for councils then cuts to early help services are inevitable across England. He said that such cuts will increase the risk of children being taken in to care and lead to a rise in spending across youth justice, social care and health in the long-term.
The proposed reductions in children's services spending are part of a wider set of cuts East Sussex County Council is planning, amid falling government funding, rising costs, an increased demand for services and an ageing population.
It is looking to make £12.3m worth of savings over the next three years and will focus on a "core offer" of services that will ensure it can meet its statutory duties. This includes protecting children and vulnerable adults. The council warns though that further cuts of up to £33.4m could be required.
"We'd all like to provide more than a core service because none of us came into politics to make cuts, but this proposal is presented as a realistic ambition in a time of austerity," said council leader Keith Glazier.
"As an efficient and well-managed council, we've shown how much we can deliver for East Sussex, even in a severe financial climate. Agreeing a basic but decent core offer will help us continue that and we'll make sure every penny spent has the greatest possible impact."
At next week's cabinet meeting councillors will be asked to approve the launch of a consultation on the "core offer" ahead of a final decision on cuts and changes to services early next year.
East Sussex's children's services were handed Ofsted's highest rating in September, with inspectors saying that "leaders and managers have successfully established a culture in which talented social workers stay, and where effective social work flourishes".