More than a quarter of children aged 14 to 16 say they often feel depressed, according to a new study by the Children's Society.
A separate online vote by CBBC Newsround released with the study found that 22 per cent said they felt bad or really bad about their health.
Many also expressed feeling under pressure to look good and 70 per cent said they dieted some or all of the time.
The Children's Society also uncovered adults' concern about children's mental health and well-being.
Just one in ten adults said they felt children nowadays are happier compared to when they were growing up.
When asked what has the most negative impact on children's well-being generally, adults rated family breakdown and conflict (29 per cent) and peer pressure (23 per cent) highly.
Commenting on the research, Professor Stephen Scott of the Institute of Psychiatry and an inquiry panel member, said: "Many respondents to the inquiry shared the belief that well being depends on good relationships, especially within the family; on a sense of purpose and on freedom.
"To achieve this, child mental health and well being must be everybody'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."
Children's Society chief executive Bob Reitemeier added: "Too often mental health and well-being have been dismissed as being of little importance but there is now an understanding that if we want to give children a better childhood these matters must be addressed.
"We now need to translate this growing concern into action and investment in the necessary support services."