Adolescent deaths

Every year, nearly 1.5 million adolescents die from substance abuse, pregnancy-related complications, suicide, injuries, and violence Adolescents account for approximately 50 percent of all new HIV infections.

Children growing up in war zones face the toughest problems but experts also warn that those in countries such as the UK are far from immune.

The report highlights big increases in depression and suicide among children and adolescents.

Children who are depressed will also be prone to other illness.

Depressive disorders are the fourth leading cause of disease and disability, and are expected to rise to second place by 2020.

Teen problem

Of particular concern are teenagers, a group which the WHO and Unicef believe is neglected by many public health doctors, but one which is more likely to suffer serious health problems than younger children.

Mental illness

Around 450 million people suffer from mental disorders. One in four families have at least one member with a mental disorder at any point in time Mental illness accounts for 12% of the total burden of disease

According to the WHO, 70% of premature adult deaths link to behaviour that develops in adolescence, such as smoking, drinking and illicit drug use.

The report also highlights a lack of progress in reducing the high death tolls among newborns, which it says has stymied progress in child health over the past two decades.

Hans Troedsson, WHO director for child and adolescent health, said: "The international health community is concerned about the mental health status of our young.

"It is a time-bomb that is ticking and without the right action now millions of our children growing up will feel the effects."

Dr Gro Harlem Brundtland, WHO director-general, said it was vital that young people were given information and help to live healthy lives.

At the UN General Assembly Special Session on Children in May, governments will be asked to commit to targets and investment in child and adolescent health programmes as part of the global child survival agenda for the coming decade.