The London Borough of Southwark said it is the first local authority to make the pledge, which compares against a national NHS England target for 2020/21 for at least 35 per cent of children with a mental health condition to be treated by a NHS community mental health service.
The decision was taken unanimously by the Southwark health and wellbeing board, which includes council representatives and local health and education professionals. No detail has yet been given on the timeframe children can expect to be treated within.
Speaking at the meeting Jasmine Ali, Southwark's lead member for children, schools and adult care, said that the council is looking for "great ideas" to achieve the commitment. A 24-hour mental health access facility is among suggestions made.
"The council, clinical commissioning group, its partners and service users need to work together to revolutionise services. I think we need to do that by raising the bar. I say we aim to meet 100 per cent of our children and our adolescents' mental health need," said Ali.
Board member and GP in the borough Dr Jonty Heaversedge says he wants to see a greater focus on preventing the need for specialised mental health services.
"What we can't do is just focus on a target for access that is just picking up the pieces," said Dr Heaversedge.
"I think there are places we can learn from in how we screen, how we identify people more effectively earlier and how we create more opportunities that are not about those specialised services like CAMHS but the sort of services that will support people much earlier to become healthier."
Speaking after the meeting Ali added: "This council has made a promise to deliver a fairer future for all and this includes recognising that mental health is just as important as physical health.
"It simply isn't good enough to say we will only treat some of the children who need mental health services. Everyone who needs support should receive it, and that's what we, with our health, education and voluntary sector colleagues, have agreed to do."
A report was also presented to the board outlining challenges facing CAMHS in Southwark and making recommendations for how access can be approved.
It revealed that the borough's specialist mental health services are seeing more children than neighbouring boroughs and that both the public and professionals found the system of referrals "difficult to navigate".
There is also a 20 per cent vacancy rate in the borough's CAMHS team, high thresholds and long waiting lists. In 2017/18 services were only able to meet the needs of 30 per cent of children with a diagnosable mental health condition, which is expected to rise 32 per cent in 2018/19.
Earlier this month official data obtained by the Children's Commissioner for England revealed that more than two thirds of the 338,000 children referred to child and adolescent mental health services (CAMHS) in 2017/18 did not receive treatment within a year.
Only half of the children who are admitted to CAMHS were seen within six weeks, the data shows.