The amount councils are spending on unaccompanied child asylum seekers has almost doubled in four years, the Local Government Association has said.
Local authorities take on the responsibility for the accommodation, living allowance, education and social worker support for children granted asylum in the UK.
This support continues in various forms until they turn 25.
The LGA is calling on the government to allocate more money to local councils to look after such children, saying councils spent over £152m on unaccompanied asylum-seeking children between 2017 and 2018.
The figure is up from £77m between 2014 and 2015.
Rising costs are contributing to a £3.1bn funding gap that will be faced by councils' children's services by 2025, the LGA has said.
Bridget Chapman of the Kent Refugee Action Network works with under-18s who arrive unaccompanied in the country seeking asylum.
While taking a group of young people on an art trip to Walmer Castle near Deal in Kent, she told Sky News she sympathises with the LGA's message, especially as, for her charges, the funds make a real difference.
She said: "That small investment made now means the young people - and they are fantastic young people - have a chance to be really successful.
"If you put in that foundation and give them the support when they need it, they're less likely to have problems later on.
"And those problems, if they have them later on, can be costly.
"So I think it is money well spent."
Saddam Aloukla, 19, is one of those who has been helped by Ms Chapman.
He left Syria aged 15 and arrived in the UK in the back of a lorry after an eight-month journey across Europe.
Mr Aloukla says the help he has received in Kent has helped set him on a path towards his dream of becoming an engineer.
He told Sky News: "The council, you know, they give me some money, and they give me some space where I can sleep, a room or something like that.
"Without that, if there was no one to support me or the younger people who arrive here, it would be difficult.
"Because we should work and we want work now because we are young.
"And we want to study and get an education.
"Without education I can't get a better job and join into the community with people, so really education is so important."
The LGA's plea for more support comes in the week that councils are due to set local budgets and council tax.
Councillor David Simmonds, chair of the LGA's asylum, migration and refugee task force, told Sky News: "Given the significant financial pressures councils are under... achieving the level of support new arrivals are legally entitled to is becoming more and more challenging."
The government is carrying out a spending review on how much it is costing councils to support unaccompanied children.
The LGA wants that review to be carried out more speedily, and for quicker decisions on which children are eventually granted asylum.
A Home Office spokesperson said: "We try to resolve cases as quickly as possible, however immigration cases can be complex and the public would expect that when granting a person the right to remain in the UK we rigorously check the information submitted.
"As a result, some applications can take longer than others."
When it comes to money, the Home Office added: "We are currently reviewing the funding arrangements... We hope to reach a conclusion soon, but it is right that we take time to thoroughly assess the evidence."
In the meantime, Mr Simmonds says changing people-trafficking trends means more councils face looking after asylum-seeking children.
He added: "Ports of entry councils like Kent, my own council Hillingdon, with Heathrow Airport, have seen huge numbers of refugee children that they're looking after over the years.
"But also as we've seen a network of traffickers developing, more and more children are being dropped off on motorway networks. So councils like Staffordshire are now supporting more than 200 children, despite not being a port authority.
"So this is an issue that's gone from being something of concern to maybe a dozen or so councils, to affecting a very large number of communities up and down the country."