Children and young people with mental health difficulties have to wait on average 10 years between becoming unwell and receiving any help, according to new findings from the Centre for Mental Health.
The Missed Opportunities report, released on Tuesday, reveals that mental health problems are very common in young people, yet awareness is poor.
The review found that most attempts by parents to get help for their children are unsuccessful, resulting in an average delay of a decade in receiving help.
This delay sees young people's mental health problems multiply and get progressively worse, eventually escalating into a crisis, the report found.
Lorraine Khan, associate director for children and young people at Centre for Mental Health, said that childhood mental health problems are "extremely common" and can be very serious.
She said that they can affect 10% of children each year, casting "a long shadow well into adult life".
“Good mental health is shaped very early on at the first spark of life.
"Childhood experiences and exposure to risks for poor mental health make some children especially vulnerable to both emotional and behavioural problems.
"And the longer they are exposed to risks such as neglect, abuse, bullying and the effects of poverty, the more their life chances are undermined," Khan said.
“Most common childhood mental health problems can be treated effectively. Early help is vital to have the best chance of success.
"There is good evidence for a range of interventions to boost children’s mental health, and the sooner effective help is offered the more likely it is to work," she added.
The delay in treating young people with mental health problems can cost society more than £105 billion a year.
It means there are an estimated 900,000 children between the ages of five to 16 who are suffering and most will do so for years before getting any support at all.
One girl, who is now 18 and wished to remain anonymous, told the Huffington Post UK how she struggled to find help.
“I just wanted someone to care and believe,” she told the Huff Post UK in February as part of the Young Minds Matter series.
“To say ‘you’re not worthless, not ugly, incapable. You shouldn’t be treated like this’. If someone just told me this, it would have made so much of a difference.”
She was six when she first showed symptoms of what she now knows was mental illness.
Today's report found that the most common mental health problems among children are behavioural problems, which severely affect one child in every 20.
Boys are more likely to have mental health problems during early years, but by teenage years girls are more likely to have emotional problems, the report reveals.
Khan said: “Schools have a particularly important role in protecting children’s mental health.
"This can be done most effectively through a ‘whole school approach’ including classroom-based skills development and awareness raising, anti-bullying programmes, raised staff mental health literacy, and speedy access to help for children who need it."
Children who have been subjected to neglect and abuse, who are bullied or who bully, and children whose parents have mental health problems are at especially high risk of poor mental health.
Groups with higher rates of poor mental health also include lesbian, gay, bisexual and transgender young people, those in the youth justice system and those who have been looked after by local authorities.
The report found that children and parents continue to encounter major barriers to finding help for mental health problems.
Meanwhile, teenagers and young adults rarely seek help from formal sources, but are more likely to turn to friends or go online.
“We need to take every opportunity to support families and schools to build firm foundations for children’s mental health," Khan said.
"We need to raise awareness of the first signs of poor mental health and reinforce the importance of getting early help.
"And we need to offer effective and young people friendly help for every child of any age at the first signs of difficulty.
“Waiting for a child’s mental health to deteriorate until it hits crisis point causes untold distress and damage to their lives and carries a heavy social and economic cost.
"We have to take action now to offer high quality help quickly to children and young people everywhere.”
Andy Bell, director of the Centre for Mental Health, said in a blog posted on the Huffington Post UK that there can be a stigma around mental health, which creates a "conspiracy of silence' for those who most need help.
He said: "There are many reasons for these long delays in getting help.
"Poor mental health literacy is a major barrier for parents, children, teachers and other professionals, causing uncertainty about whether there is a need to seek help.
"For teenagers, stigma can create a 'conspiracy of silence' that prevents them from disclosing distress. And even when young people do get help, they report finding services off-putting, unappealing or frightening."
Useful helplines and websites:
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