The delights of our children's lives are visible to us all and, indeed, are often envied by older generations. Toys, holidays and a bedroom of one's own are the lot of many children nowadays. Girls in particular seem to be flourishing in recent decades, enjoying opportunities previously denied to them. The improvements in the care and well-being of children in hospital and of children with disabilities of all kinds are enormous.

Yet a succession of reports focusing on the well-being and perceived happiness of children and young people has painted a dismal picture. Tomorrow will see the publication of the Good Childhood report, two years in the making and expected to lament the lack of outdoor play. Most famously, the 2007 Unicef report placed the welfare of British children bottom in a list of 21 rich countries.

Evidence of increased levels of childhood depression and other serious mental health difficulties continues to emerge. Children's writers, including Philip Pullman, and an array of champions of childhood have protested about the strains on young people today. So are children unhappier now than in the past? And if they are, what can be done about it?

Our clinical experience as child psychotherapists working in the NHS tells us that children often find life complicated and stressful. The pressures of competitive consumerism, of changing family dynamics and greater social inequality are felt by children as well as adults and they are less well-equipped to deal with them. The current economic downturn will worsen this situation, since the atmosphere of widespread gloom and anxiety will seep into children's minds without their having the resources to understand what is happening.

Also relevant is how exposed today's children are to the grimmer realities of the world. Television and the internet provide little protection from images of disaster and distress. The visual nature of our culture bombards children with levels of violence and human vulnerability that have complex effects on their picture of the world. Some clinical problems, such as anorexia, seem particularly exacerbated by the focus on how we look and others, such as conduct and attention disorders, are in part the outcome of over-stimulation by objects and images unmediated by adult company.

Clinicians increasingly report of children whose imagination is wholly derivative and who have little expectation of anyone being interested in them. Alongside this is the implication that everything can be fun, that we should be happy all the time and that all frustrations can be removed. This conjunction of a knowledge of human misery with a surrounding ideology of all things being possible is hard to make sense of.

Ordinary unhappiness is not always easily distinguished by parents or young people from the extraordinary, but long-lasting moods of sadness, anxiety or confusion and difficulties in making friends or in learning suggest a child is in trouble.

Today's parents have a strong sense of personal responsibility for their children's chances in life. This provides for an enriched development of the individual child. But the weight of parental responsibility can be heavy and may influence increasing medicalisation. The expansion of the "diseases" of childhood - attention deficit hyperactivity disorder, autistic disorders and now bipolar diagnoses - goes along with the idea of a normality that can be achieved by psycho-pharmacology. A recent report noted that 345,000 children in the UK are now taking Ritalin to control impulsive behaviour.

Parents, professionals and policy-makers involved in children's care and education need to think much more about the support children require. Their emotional development, their growing up with a capacity for happiness and for the strength to bear unhappiness hang on their need to be accompanied by adult minds, to be thought about day-to-day. Children left to fend for themselves psychologically are no better off than those left to fend for themselves physically.

A child learns how to be self-sufficient gradually and needs grown-up help to do so. Much as we would like children to be happy, the fact is that they are born to the human condition and, as Blake said: "Joy and woe are woven fine." While part of our job is to contribute to our children's happiness, an equal part is to help them with the heartbreaks of everyday life. We cannot always get rid of their pain and struggles, but we can keep them company and feel for them.

A grieving child one of us saw last week sobbing in the park from the sudden memory that her mother was with a newborn sibling while she was being looked after by grandparents needed to be allowed the space to cry. She found eventual comfort in a conversation about Mummy's special talents after the long minutes of unhappiness had been shared.

It is certainly no help when adults are too preoccupied or too absent to register the ups and downs of children's feelings, but there is something else even more damaging to a child. This is to ask him or her to bear anxieties that properly belong to the grown-ups.

Significant numbers of families require outside support to function effectively and they must not be failed by the services provided to help them. In child and adolescent mental health services, in schools and the wider community, there is the threat of dominance by an ideology of quick-fix, rather than individual responses to a child's difficulties.

Complexity and depth are minimised, but to minimise is as dangerous as to exaggerate. There is an assumption that if your troubles can be explained to you they will cease to worry you. This ignores our awareness that difficulty can never be overcome without struggle.

What makes children unhappy is to ask them to carry loads that are beyond their strength. Too many children are in this position. They need grown-ups able to demonstrate that painful experiences can be coped with and able to protect them from being weighed down with anxieties that are too much for them. That leaves room for happiness and ordinary, manageable unhappiness.

• Lisa Miller and Margaret Rustin are consultant child and adolescent psychotherapists at the Tavistock and Portman NHS Foundation Trust