Depression may be widespread among children
Depression symptoms could be a problem for large numbers of teenagers, suggest surveys for the Children's Society.
More than a quarter of 14 to 16-year-olds questioned said that they frequently felt depressed.
A leading child psychiatrist said more support, and resources, for parents was essential to tackle the problem.
But one adolescent mental health specialist said children who described feeling sad, even regularly, may not actually have a depressive illness.
In 2007, UNICEF rated the UK bottom of a league of industrialised countries for child well-being, saying our children were under-educated, unhappy and unhealthy compared with other European countries.
Results from the surveys, one by NOP of 8,000 teenagers, and another conducted by BBC's Newsround programme, were published as part of the society's report into child health.
A total of 27% of those questioned agreed with the statement: "I often feel depressed".
In the Newsround survey many children said they felt under pressure from school, their classmates, and family expectations.
Seven out of ten said they felt the need to "look good", and were on a diet some or all of the time.
The society's chief executive Bob Reitemeier said that the mental symptoms of children had often been "dismissed".
"There is now an understanding that if we want to give children a better childhood these matters must be addressed.
"There is a growing recognition of the true cost of neglecting children's mental health and wellbeing."
Professor Stephen Scott, from the Institute of Psychiatry, and one of the contributors to the inquiry, said that child mental health should be "everyone's business".
"Support for parents is crucial - schooling has a key part to play, and providing the effective treatments now available for children with mental health problems takes time, skill and resources."
Marjorie Wallace, the chief executive of Sane, said: "We know that one in ten young people have a mental disorder of some kind and it is concerning that over a quarter of young people in this survey say they often feel depressed.
"It is vital that all children and young people with mental health problems are identified and treated from the earliest stage."
Anita Thapar, Professor of Child and Adolescent Psychiatry at Cardiff University Medical School said that research pointed to between 2% and 8% of children being depressed, depending on their age and social circumstances.
"This is probably what I would describe as low mood, although some of the children who say they are feeling like this may well be suffering from a depressive disorder.
"I would ask, is this a transient or persistent low mood with other symptoms which are getting in the way of life?"
Children's Minister Kevin Brennan said that other national surveys suggested that children generally felt well and good about themselves. He said: "But that doesn't mean that there aren't problems and also some new challenges to face in the modern world.
"That is why we issued our Children's Plan, which aims to make this the best place in the world to be a child."