The UK has been accused of failing its children, as it comes bottom of a league table for child well-being across 21 industrialised countries.
Unicef says the study is the first of its kind for child well-being
Unicef looked at 40 indicators from the years 2000-2003 including poverty, family relationships, and health.
One of the report's authors told the BBC that under-investment and a "dog-eat-dog" society were to blame for Britain's poor performance.
The government says its policies have helped to improve child welfare.
Unicef - the United Nations children's organisation - says Child Poverty in Perspective: An Overview of Child Well-being in Rich Countries is the first study of childhood across the world's industrialised nations.
In its league table the Netherlands came top, followed by Sweden, Denmark and Finland.
Unicef UK executive director David Bull said all the countries had weaknesses that needed to be addressed.
"By comparing the performance of countries we see what is possible with a commitment to supporting every child to fulfil his or her full potential," he said.
The authors say they used the most up-to-date information to assess "whether children feel loved, cherished, special and supported, within the family and community, and whether the family and community are being supported in this task by public policy and resources".
But they added: "The process of international comparison can never be freed from questions of translation, culture, and custom."
Professor Jonathan Bradshaw, from York University, one of the report's authors, put the UK's poor ratings down to long term under-investment and a "dog-eat-dog" society.
"In a society which is very unequal, with high levels of poverty, it leads on to what children think about themselves and their lives. That's really what's at the heart of this," he said.
The UK government said its initiatives in areas such as poverty, pregnancy rates, teenage smoking, drinking and risky sexual behaviour had helped improve children's welfare.
Welfare reform minister Jim Murphy said the Unicef study was important, although it used some data which was now out of date.
CHILD WELL-BEING TABLE
9. Republic of Ireland
15. Czech Republic
20. United States
21. United Kingdom
"Hopefully it leads to a wider conversation about what more we can do to eradicate poverty," he said.
Unicef's league table drew on sources including the OECD Programme for International Student Assessment (PISA) and the World Health Organization's survey of Health Behaviour in School-age Children (HBSC) aged 11, 13 and 15.
For the UK, the HBSC survey is taken from responses of residents of England only. Unicef also said some PISA indicators for the UK should be treated with caution because of low sample response rates.
The Children's Society launched a website to coincide with the report, www.mylife.uk.com, which allows children to answer a series of surveys about their lives.
Chief executive Bob Reitemeier said: "We simply cannot ignore these shocking findings.
Family and peer relationships
Health and safety
Behaviour and risks
Own sense of well-being [educational]
Own sense of well-being [subjective]
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"Unicef's report is a wake-up call to the fact that, despite being a rich country, the UK is failing children and young people in a number of crucial ways."
The Children's Commissioner for England, Professor Sir Al Aynsley-Green, said: "We are turning out a generation of young people who are unhappy, unhealthy, engaging in risky behaviour, who have poor relationships with their family and their peers, who have low expectations and don't feel safe."
UK REPORT FINDINGS
UK child poverty has doubled since 1979
Children living in homes earning less than half national average wage - 16%
Children rating their peers as "kind and helpful" - 43%
Families eating a meal together "several times" a week - 66%
Children who admit being drunk on two or more occasions - 31%
Colette Marshall, UK director of Save the Children, said it was "shameful" to see the UK at the bottom of the table.
Shadow Chancellor George Osborne accused Chancellor Gordon Brown of having "failed this generation of children".
"After 10 years of his welfare and education policies, our children today have the lowest well-being in the developed world," he said.