Research by The Children's Society found that, in relation to 30 different aspects of life, 10- and 12-year-old children in England are unhappier than those in 11 other countries including Uganda, Ethiopia and Algeria.
English children only fared better than children in Germany, South Korea and Estonia in the 15-country study - The Good Childhood Report 2015.
The report found that more than a third (38 per cent) of 10 and 12-year-olds in England had been physically bullied in the last month, and half (50 per cent) had felt excluded.
The research found that children in England who were bullied frequently were six times more likely to have low wellbeing than children who have not been bullied.
"Bullying emerged as a key issue in England in comparison to other countries, particularly with regard to emotional bullying," the report states.
"More than a third of children bullied four or more times in the last month had low levels of life satisfaction, making them more than six times more likely to have low life satisfaction than those who hadn't been bullied at all."
The study is now in its 10th year. Until 2008, evidence suggested that overall children's wellbeing was improving, but since then improvements in overall life satisfaction have stalled.
The Children's Society is calling on government make it a legal requirement for schools in England to provide counselling to pupils, which would bring it in line with Wales and Northern Ireland.
Matthew Reed, chief executive of The Children's Society, described the findings as "deeply worrying".
He said: "School should be a safe haven, not a battleground.
"Despite a long period of austerity, we are one of the richest nations in the world yet the happiness of our children is at rock bottom.
"They are unhappy at school and are struggling with issues around their appearance and self-confidence.
"We know that this is related to their mental health and can prevent them flourishing. We need to urgently find a way to make young people feel happier about their lives to avoid storing up problems for the future."
Jonathan Bradshaw from the department of social policy and social work at the University of York, which collaborated with The Children's Society on the report, said: "We need to make more effort to monitor the wellbeing of our children and we need to devote more resources to understanding how they are doing and to ensuring that their childhood is as good as it can be."