Children growing up in the United Kingdom suffer greater deprivation, worse relationships with their parents and are exposed to more risks from alcohol, drugs and unsafe sex than those in any other wealthy country in the world, according to a study from the United Nations.

The UK is bottom of the league of 21 economically advanced countries according to a "report card"' put together by Unicef on the wellbeing of children and adolescents, trailing the United States which comes second to last.

Today's findings will be a blow to the government, which has set great store by lifting children out of poverty and improving their education and prospects. Al Aynsley Green, the children's commissioner for England, acknowledges that the UN has accurately highlighted the troubled lives of children. "There is a crisis at the heart of our society and we must not continue to ignore the impact of our attitudes towards children and young people and the effect that this has on their wellbeing," he says in a response today.

"I hope this report will prompt us all to look beyond the statistics and to the underlying causes of our failure to nurture happy and healthy children in the UK. These children represent the future of our country and from the findings of this report they are in poor health, unable to maintain loving and successful relationships, feel unsafe and insecure, have low aspirations and put themselves at risk.

"It is time to stop demonising children and young people for what goes wrong and start supporting them to make positive choices. To bring an end to the confusing messages we give to young people about their role, responsibility and position in society and ensure that every child feels valued and has their rights respected."

The Unicef team assessed the treatment of children in six different areas - material wellbeing; health and safety; educational wellbeing, family and peer relationships, behaviours and risks; and the young people's own perceptions of their wellbeing.

The Netherlands tops the league, followed by Sweden, Denmark, Finland and Spain. The bottom five are Portugal, Austria, Hungary, the US and the UK.

Nine countries, all of them in northern Europe, have brought child poverty down below 10%, the report shows. But it remains at 15% in the three southern European countries - Portugal, Spain and Italy - and in the UK, Ireland and the US. Child poverty is a relative measure that shows how far their standard of living has fallen below the national average.

The Unicef report adds: "The evidence from many countries persistently shows that children who grow up in poverty are more vulnerable: specifically, they are more likely to be in poor health, to have learning and behavioural difficulties, to underachieve at school, to become pregnant at too early an age, to have lower skills and aspirations, to be low paid, unemployed and welfare-dependent."

The Conservatives seized on the report, claiming that it endorsed their attack on the way in which Gordon Brown had addressed the issue of child poverty, and the prime minister had demonised the role of children in his drive against antisocial behaviour.

The shadow chancellor, George Osborne, said: "This report tells the truth about Brown's Britain. After 10 years of his welfare and education policies, our children today have the lowest wellbeing in the developed world."

Labour said it had taken 700,000 people out of child poverty and was mounting an unprecedented investment programme in a network of children's centres. A government spokesman argued that in many cases the data use d in the report was several years old and "does not reflect more recent improvements in the UK such as the continuing fall in the teenage pregnancy rate or in the proportion of children living in workless households".

Some of the most shocking findings concern the relationships children and adolescents have with their family and peers. The UK is bottom of the 21 countries.

This, says Unicef, "is as difficult to measure as it is critical to wellbeing".

To attempt to score countries, the experts have focused on children's own reports of how much time their parents spend "just talking" to them, how many say they eat the main meal of the day with their parents more than once a week and the percentages of 11, 13 and 15-year-olds who find their peers "kind and helpful". UK parents do reasonably well on "talking regularly" - 60% of children say they chat, putting Britain 12th in the league table. But while a similar proportion say they eat together more than once a week, the UK lags towards the bottom of the league, with Italy, Iceland and France at the very top end.

The report presents a sad picture of relationships with friends, which are so important to children. Not much more than 40% of the UK's 11, 13 and 15-year-olds find their peers "kind and helpful", which is the worst score of all the developed countries.

The UK takes bottom place "by a considerable distance" for the number of young people who smoke, abuse drink and drugs, engage in risky sex and become pregnant at too early an age. For 16 out of 17 OECD countries with the data, between 15% and 28% of young people have had sex by the age of 15. For the UK, the figure is 40%.

On education, the UK comes 17th out of 21. At the age of 15, British children score relatively well on reading, mathematical and scientific literacy. But more than 30% of 15- to 19-year-olds are not in education or training and are not looking beyond low-skilled work.