One in 10 young people suffers from significant mental health problems, a leading children's charity claims.
One in ten children have a mental health disorder, the NCH says.
The NCH said it found the prevalence of emotional problems and conduct disorders had doubled since the 1990s, citing studies of 8,000 children.
But some experts cast doubt on the NCH's interpretation of the findings and its definition of a "disorder".
The final findings of the studies are due to be published later this year, when the NCH launches a major campaign.
Chicken or egg
The NCH defined an "emotionally well" child as one who demonstrated empathy, self-awareness, an ability to manage feelings, motivation and good social skills.
It based its conclusions that this wellbeing was deteriorating on three studies carried out in recent years.
The charity also carried out a survey "to test and compare our research findings with the experiences and views of the general public".
It found that the public believed emotional wellbeing was more important than family income, physical health, and IQ.
Clare Tickell, chief executive of the NCH, said: "The lack of emotional wellbeing amongst our children and young people is undermining the foundations of any social policy to combat social exclusion, deprivation or lack of social mobility."
But Professor Sue Bailey, chairwoman of the Child and Adolescent Faculty at the Royal College of Psychiatrists, said all these issues were intertwined.
Poverty and exclusion, she said, were inextricably linked with the state of a child's wellbeing.
She added that she was familiar with the one in 10 figure for mental health disorders, adding that this "was not new", but said it covered a range of problems - from the very minor to the very serious.
She backed a statement by the Children's Minister Beverley Hughes, who said that the available figures did not back up NCH claims that incidences of childhood depression were rising.
"In fact, they show that the prevalence of mental disorders among five to 16-year-olds in 2004 have remained broadly unchanged from the previous survey in 1999."