Services for children with mental health problems need a "complete overhaul" so youngsters and their families are not forced to deal with a complex system at such a difficult time in their lives, council leaders have said.
The current "fragmented" system means that children are forced to navigate a myriad of different mental health organisations to access care, t he Local Government Association (LGA) said.
Difficulties in understanding how the system works can make it "complicated to get help", the LGA said.
Families should not have to cope with a complex system at such a challenging time, said the association - which represents almost 400 councils across England and Wales.
The LGA also raised concerns that children and young people in need of care are "falling through the gaps" because of funding problems in the NHS.
It said that " only full reform of the mental health system can now ensure improvement".
David Simmonds, chairman of the LGA's children and young people board, said: "Looking after young people is the most important thing councils do and it is all of our duty to make sure that children, along with their mums and dads, have access to the services they need .
"It is totally unacceptable that vulnerable young people who need help can end up falling through gaps in the system being widened because of funding pressures which are fuelling long NHS wait times.
"Local authorities still have serious concerns about mental health funding for children and want a complete overhaul of the fragmented and complex system that they currently face each day when trying to access services delivered by the NHS and other partners.
"Councils have worked hard to protect the many services they provide for vulnerable children but in the face of 40% cuts to local government, this has becoming increasingly challenging.
"Councils are committed to change and are already playing their part, but there are vital changes to the system that need to be made.
"It is absolutely crucial that the whole system is properly funded, resourced and joined-up to ensure young people receive the very best services available."
Sarah Brennan, chief executive of mental health charity YoungMinds, added: " We welcome the LGA highlighting that the mental health system for children and young people is extremely fragmented in many places and to warn of the dire funding situation.
"Every day we hear from parents, through YoungMinds Parents' Helpline, desperate for help for their child.
"They either cannot access services or they are stuck for months on a waiting list. Clinicians tell us that their services are at breaking point.
"As a result they are forced to increase thresholds, which means only the children with the most severe illness receive care.
"There is overwhelming evidence to suggest that if we get it right for children and young people, we will greatly reduce the burden of mental health for future generations."
A Department of Health spokeswoman said: " We want to make sure that children get the mental health care they need.
"We are taking immediate action by making more beds available and the taskforce we are appointing will improve commissioning and create more joined-up services for children and young people.
"We've invested £54 million to help children get specialist treatment and are scrutinising NHS spending to make sure that mental health is given the priority it needs.
"We are absolutely determined to get this right so that children everywhere get high-quality care."