Girls are becoming increasingly distressed, with more than a quarter of a million girls now saying they are unhappy with their lives, according to new research.
The Good Childhood Report, produced by The Children's Society and the University of York, highlights a growing gender gap in children's experience of life.
It estimates that 14 per cent of girls aged 10 to 15 are unhappy with their lives as a whole compared to 11 per cent five years' ago. During the same period, the proportion of boys who are unhappy has remained stable at 11 per cent.
And the researchers found that the difference was even starker when they asked young children about their looks: more than one third (34 per cent) or girls were unhappy with their looks, compared with 30 per cent five years' ago. Again the proportion of boys who were unhappy with their appearance (20 per cent) has remained stable.
The report points out that girls are more likely than boys to experience emotionally bullying, such as name calling, and that previous research suggests girls are more likely to spend extended periods on social media.
Matthew Reed, chief executive of The Children's Society, said: "It is desperately worrying that so many of our young people are suffering rather than thriving. Girls are having a particularly tough time and it's clear that concerted action is needed to tackle this problem."
The report calls for the government to make it a legal entitlement for children to be able to access mental health support in schools and colleges.
A government spokesperson said: "We want every young person to grow up feeling supported and confident about their future. We are working with schools, parents and the media to help improve young people's resilience, boost their confidence and tackle bullying.
"The right help for young people is vital which is why we are working to improve the mental health support available as part of an ambitious five year programme backed by an additional £1.4 billion investment."
The Good Childhood Report has been published since 2012. It uses evidence from regular surveys of 2,000 households, three school-based surveys involving more than 17,000 chilren and an existing longitudinal study of 40,000 households.
In a separate study, also published today, children as young as three are showing signs of being unhappy with their appearance and bodies.
Almost a third of nursery and school staff said they had heard a child label themselves fat while 10 per cent said they had heard a child say they felt ugly, a survey of childcare professionals has suggested.
The survey of 361 children was carried out by the Professional Association for Childcare and Early Years (Pacey).
An adviser to the group, Dr Jacqueline Harding, said more research was needed in the area but speculated "contributing factors" were likely to include television and images in story books and animations.
The research comes after a government study last week revealed that more than one in three (37 per cent) teenage girls suffers from "psychological distress" by the age of 14.