Pupils should be given lessons on mental health, it has been suggested, amid fresh concerns that many youngsters are affected by the issue.
Campaigners are calling for the topic to be included in the national curriculum and for schools to provide counselling and support to any young person that needs it.
Around one in five children has symptoms of depression, such as continually feeling low or sad, helpless or anxious, according to a survey for MindFull, a new mental health charity.
Nearly three in 10 of the young adults questioned said they had harmed themselves on purpose before they were 16 because they felt down.
Nearly a third (32%) said they had thought about or attempted to end their own life when they were younger, the charity claimed.
The survey questioned more than 2,000 16 to 25-year-olds about their experiences of mental health when they were children.
It suggests that many young children feel down because of stress at school, because they are worried about their future and because they feel they are not good enough.
The effect of mental health problems has a knock-on impact on young people's lives, the charity said, with youngsters suggesting that it affected their school or work life, their concentration or made it hard for them to leave the house.
More than three in five (61%) of those who said they had had a mental health problem said they had skipped school or college when they were under 16 because of how they were feeling.
The charity, which has won the backing of Labour leader Ed Miliband and psychologist Tanya Byron, said there were fears that young people are not getting the support they need.
Just over half (52%) of those who said they had suffered from mental illness said they felt let down by the support they were offered, while 47% of those who had symptoms of depression and spoke to someone about it said they never got the help they wanted.
Nearly two-thirds of young adults said that including mental health on the national curriculum would help to tackle the issue, while a similar proportion (62%) backed having a dedicated person to look after pupils' mental health in every secondary school and 67% said there should be training for teachers.
Emma-Jane Cross, chief executive and founder of MindFull, said: "Too many children who try to speak out about the way they're feeling are being let down or simply ignored. It's unacceptable that so many are having to resort to harming themselves on purpose in order to cope, or worse still are thinking about ending their own lives.
"Early intervention is proven to help prevent adult mental health problems, so swift action must be taken now if we are to avoid a legacy of serious long-term mental illness."
The charity, which is launched on Friday, said it will be working with schools to educate young people on how to cope with mental health issues. It will also offer 11 to 17-year-olds access to free online professional counselling and advice.
Lucie Russell, director of campaigns and policy at the YoungMinds charity, said: "Children and young people are growing up in a toxic climate ... they exist in a 24/7 online world where they never switch off, where cyberbullying, consumerism and pornography, sexting and the pressure to have the perfect body bombard them daily, where any exam grade below a C means failure and employment prospects are bleak.
"We know from our extensive work with young people that the support they so desperately need when they aren't coping is grossly lacking but we also know from services that they're under huge funding pressures and are overwhelmed with demand.
"We very much welcome MindFull's new online service for young people which will get support to young people where they are, when they need it and we hope MindFull will work with us to get the vital importance of children and young people's mental health up the political agenda both locally and nationally."
Useful websites and helplines:
Samaritans, open 24 hours a day, on 08457 90 90 90
Mind, open Monday to Friday, 9am-6pm on 0300 123 3393
Students Against Depression, a website by students, for students.
HopeLine runs a confidential advice helpline if you are a young person at risk of suicide or are worried about a young person at risk of suicide. Mon-Fri 10-5pm and 7pm-10pm. Weekends 2pm-5pm on 0800 068 41 41
Mental Wealth UK To join the community or launch a student group contact the charity on home@mentalwealthuk.com