IT'S BREAKFAST time, and you're trying to focus on dishing up cereal, making school lunches, finding clean under wear and missing shoes - when you hear a low snarl, followed by the thump of running feet and a slammed door.

You try turning the soothing tones of David Hanly up a decibel or so to avoid the fight, but of course you can't. The alleged injured party storms into the kitchen swearing vengeance, demanding justice.

Another day, another battle in the war zone your home has become.

If we're lucky, this is a scene we might witness, say, once a week, and not once a day. For it is a pretty universal truth that brothers and sisters fight, and any parent who says differently is probably lying - or so blissed out on Prozac or Valium they've stopped noticing.

The fact is, kids fight quite a lot and at a certain low level, it's just part of the background noise, just about tolerable, if at times really annoying. But at various stages in the life of a growing family, the battles may escalate, they may become continuous, the fighting may become a continual source of stress on both parents.

The childcare books tell you to let them sort it out themselves, and you try to follow that advice. But whether you step in to separate the feuding parties or stand back, it can be very, very wearing.

Do you have to live with it, or is there anything you can or should do about it?

Anne and her husband have opted to live with the continual fighting between their two children, a boy aged 15, and a daughter 19, though it is so persistent it makes the couple really miserable.

"He'll decide he wants the room to himself to watch TV and he'll try to turf her out; she always confronts him, never gives way. Or he'll be getting ready to go out and she'll say something insulting. In one way or another, the fights are all territorial, or about possessions. Let's say I buy a packet of biscuits; she'll act like they're hers, he'll get cross, and off they go.

Her son and daughter don't fight physically. They scream loudly and constantly at each other, to the point where Anne is really worried what the neighbours think. It takes the joy out of daily life, and makes it hard for the couple to go away by themselves, even for a day, because they don't feel they can trust the kids to get on.

Anne and her husband are far from alone. "It's just so depressing, and so unremitting," another mother says. "The squabbles start when they get up, and they go on nonstop." Both mothers agree that holidays away are worse: enforced togetherness just highlights the problem.

Valerie Smith of Parentline, the helpline service for parents under stress, says calls are about the issue of children fighting. Sometimes, especially if their children are very young, parents need to be reassured that children's aggressive behaviour is normal: "Some parents fear that they have a monster in their midst, and they're afraid to talk to other people."

Other parents have stood back, assuming the fighting was normal sibling rivalry, and now find it's getting out of hand. Sometimes it affects the parents' own relationship, as they fight about how to deal with the problem.

"In a lot of cases, a parent will come in and see us; we might talk about what else is going on their home," Smith says. "A third person can be objective, might spot some causes of the continued fighting - it might relate to children's relationship with their parents, it could be something in school. You can talk about ways of appealing to the children to control the fighting in the interests of the family as a whole."

Senior child psychologist Andrew Conway suggests it might be useful for parents to think of themselves as Andy O'Mahony on RTE radio's Sunday Show. He controls heated debates with an insistent "one voice, one voice please!"

"That's a very good model of debate: verbal fighting is part of growing up, of jostling for position, setting controls within a family - and a good verbal fight can clear the air." The word "argument" is better than "fight" for this kind of confrontation, Conway says. Instead of roaring at them to shut up, it might be better to get them to raise the tone. (Children and teenagers seem to delight in a kind of low repartee - "I'm not a pig", "Yes you are", "No I'm not" - that parents find tooth grindingly painful.)

Generally speaking, says Conway, the fighting that most parents are talking about is verbal, not physical; if your child is still very physically aggressive at age nine, 10, 11 or older, you should look for advice.

CONWAY SAYS parents should address a situation where the hostility between children is unremitting. This needn't mean getting professional help; maybe a concerted effort by parents is required to get to the root of the problem.

"It might be that one child has difficulty negotiating what the Americans call `human relationship skills', and fights with everybody. There may be unresolved issues of jealousy, rivalry, hate. The child giving a lot of stick may not realise the effect he or she is having. You should focus on feelings, try to get them to understand the feelings of the victim."

There is a bottom line, says Conway: "If it's getting to you as a parent, it's a problem that should be addressed."

Professional advice may be called for if you perceive that a reason for the fighting is one of your children being persistently angry, if their anger is irrational. (That's not the "I wanna watch The Simpsons", "you took my best shirt/toy/crayons" kind of anger, says Conway, but something unprovoked.)

"A child 11 years old and up who is persistently angry can terrorise his or her family; sometimes, they're the children at risk for drug abuse, or it could presage mental illness. Where a family finds it's caught up in a `walking on eggshells' syndrome, they have to do something - you just can't put up with that."