CHILDREN / Why some siblings are more equal than others: Favouritism is more common than parents admit - or are aware of. Cherrill Hicks on its causes and effects

Most parents would firmly reject any suggestion that they are more sympathetic to one child than another. 'There are no favourites in this family. You're all treated equally' is a standard refrain.

Yet research has shown that what psychologists call 'differential treatment' of siblings is surprisingly common. Judy Dunn, Professor of Human Development at Pennsylvania State University, who has studied sibling relationships, says that in many families there are significant differences in the parental affection, attention and discipline that children receive. Differential treatment, she believes, could partly explain why many siblings grow up to be strikingly unlike one another, despite sharing the same genetic heritage and environment.

Children, says Professor Dunn, are acutely aware of distinctions in parental attitudes: from an early age they monitor, and react to, not only a parent's response to them but also his or her interactions with other offspring. 'Parents might think a two-year-old can't notice what is going on but children are very sensitive. It's not just how much they are loved but how much they are loved in relation to Tommy.' The 'least favoured' child, she says, may either internalise its feelings, becoming anxious and neurotic, or externalise them into aggression and other 'conduct disorders'.

Few parents set out to favour one child

over another, so how does differential treatment develop? Peter Stratton, a family therapist and developmental psychologist at Leeds University, says that it can often be triggered by something quite trivial. 'It doesn't come about because the child is bad or the parents malicious. It's almost like an unfortunate accident which develops into a behaviour pattern within the family.

'A child may not be the sex the parent wanted; or he or she may unconsciously remind them of someone in the family they don't like; or he may be born at a time of particular stress,' he says. 'One child can also become a scapegoat for difficulties in the marital relationship. The parents may not mean to treat the child differently, but their irritation affects the way he responds and what he learns about his role in the family. The process feeds on itself: an attitude towards one child builds up and the family drifts along with it. Later, no one has any idea where it started; all the child knows is that his place is in the wrong.'

Once parents decide that X is bad and Y is good, the belief tends to be self-fulfilling, he believes. 'If X leaves his room in a mess, he's bad. If Y does the same, the attitude is that 'boys will be boys'. And parents can't see that X is taking the blame for everything.'

Sometimes a lack of sympathy for a child may be due to a clash of temperament. 'You may be the kind of parent who is very confident and outgoing and wants to take your baby to Timbuctoo,' says Penelope Leach, a specialist in child development. 'But you may happen to get a baby who is shy, easily upset and happier when handled only by one person. It's a personality mismatch - and it's nobody's fault.'

Some families, she says, go through phases where there always seems to be one child who makes trouble. 'It's important not to get in a panic about it, or to worry that you 'don't like' your child. The important thing is to be scrupulous about your behaviour.'

First-born children are often subjected to less favourable treatment when a second

baby arrives. Expected to grow up overnight and to accept the new arrival without complaint, they may rebel by behaving badly. 'Quite a lot of parents find the aggression and jealousy from an older child to a new baby intolerable, and can't cope with the strength of their feelings,' says Penelope Leach. 'To have a two-year-old around whom you can't trust not to hurt the baby can bring out the fiercest feelings - 'I feel like killing her if she makes my baby cry.' '

Parents who were anxious with their first child, she says, are usually more relaxed about their second and third; because the latter respond positively to this, they are then seen as much 'easier' than the first.

Anne Nolan, a journalist in her mid-forties, found herself preferring her second son, Ed, over his elder brother, James, born four years previously. 'The younger one was charming, funny and easy,' she recalls. 'The older one was wakeful, highly strung, with a mercurial temperament: he used to come home from school and have these terrible tantrums, throwing things around. I had this lovely tranquil younger baby and I used to dread the older one coming home. It was never that I didn't love him, but I didn't enjoy him.'

Looking back, she finds the differences in her children's personalities unsurprising. 'It was the Sixties when we had the older one and he had a fairly chaotic upbringing: I had a hectic job, I travelled all over the place, and he was being dragged across London to a child-minder when he was two. The younger one had a much calmer upbringing.

'The older one is also more like me in character. We have the same bloody-mindedness, the same rages, the same severe lack of confidence. Perhaps I saw my own unattractive qualities in him and didn't like them.'

Gender can also trigger differences in treatment. Dr Stratton says: 'Many people are disappointed to get a girl, still. And later on boys get away with more. They're expected to be boisterous and get into trouble, but this is felt to be inappropriate for girls. Our society is far more worried about girls who misbehave.'

Jane Wanford, a professional dancer of 34, says her family was bitterly disappointed that she was not a boy. 'My father's family was Jewish, my mother's Spanish, and in our family the first-born was supposed to be male,' she says. 'When my father phoned the hospital and they told him it was a girl, he said, 'No, there must be some mistake'. He was devastated. Of course, they made it into a family joke.'

Her two younger brothers, now 28 and 23, were expected to go on to further education. 'But when I wanted to stay on for college, they said no, the money has to be found for your brothers. My brothers both failed their 11-plus and didn't go to college anyway.'

Her parents, she says, give her brothers a lot of money. 'We're all self-employed, they have businesses and my parents help them out occasionally. But being self-employed as a dancer doesn't count. If they turn up with something for me, they charge me for it.'

Her father, she thinks, eventually came to terms with the fact that she was a girl. 'But my mother had a younger brother who was treated as a wonder boy. During the war she was sent away as an evacuee, but her brother wasn't. That cut very deep. She always said she would never do anything like that to her children. Intellectually, that is what she believes, but, emotionally, she wasn't able to sustain it.'

Janine Stanberg, a child psychotherapist based in London, says that unresolved issues from a parent's own childhood can result in favouring one child less. 'If you don't feel good about yourself as a woman you may not feel good about having a daughter,' she says. 'Or you may overcompensate for what you didn't have, so that the daughter becomes a little princess - and the son gets left out.

'If you were a second child, you may treat your second child the same way you were treated: 'I had a clever bigger sister and I was always shy so that's how my second child will be.' Or you may overcompensate so that the first child misses out. How much parents identify with and project on to their children is crucial.'

So how can parents avoid treating one child less favourably than another? Parents, says Stanberg, will insist that they have no favourites. 'But it is healthier to admit being more drawn to one child than another, at least to yourself. Then you can try to do something about it. You can watch yourself, the tone of voice you use. You can try to set aside time with the 'least favoured' child, try to appreciate the qualities that child has, even though he or she may not fit into your ideas of academic success, for example.'

Peter Stratton believes that it is not difficult for parents to 'unhook themselves' from certain patterns of behaviour, perhaps with professional help, or simply by taking an objective look at their behaviour. But, he warns, if they allow a pattern of differential treatment to continue, 'the least-favoured child will want their own children to provide them with the adoration they never received. And children can never meet those needs, of course - so they in turn take the blame.'