As he carried the breakfast into the bedroom, my husband announced that Alice had something to tell me. But Alice, three years old and trailing behind, was in no mood for confession. 'I didn't do it, Mummy,' she urged in a desperate attempt to wipe the slate clean before it had even been chalked.

Of course, it was silly of us to fit new sofa covers at all. Even more ridiculous to think they would last three days without being defaced by one or other of our small children.

But I had not expected Alice to add her monogrammatic touch in Biro quite so liberally or so soon. I did not know what to do when faced with a toddler who only kind of understood that she shouldn't write on settees and who was willing to persuade herself she hadn't done it anyway.

When my children spill their milk, I try not to cry about it metaphorically or literally. I hand them the cloth, until they eventually get the idea and run to fetch the cloth themselves. The moral is that we all make mistakes, and it's the mending that counts. But I could hardly expect a three- year-old to scrub her own graffiti from a set of expensive loose covers.

As I bent over the sink with the Complete Valet's Guide to Spots and Stains, it occurred to me that this is what bringing up children is about: not only the times when they smile like angels and do your bidding, but the crises of disobedience and misunderstanding. What was I going to do now?

How to discipline children is a question parents face every day. The tantrum in the supermarket, the digging-up of dahlias, the digging-in of heels - these are the encounters that challenge us to come down heavily or not at all.

In the media, the debate is often polarised and simplistic. Commentators ask whether there should be strictness or permissiveness. Government ministers seem to have decided that punishment systems are the stuff that discipline is made of. What we need is control, they say, and more of it.

But few parents can afford the luxury of backbench theorising. Discipline is a front-line job that demands detailed and instant decision- making. Every move on the part of the child can become the parent's dilemma: should my teenager be allowed to a wear a mini-skirt? Am I weak for letting my son talk to me like that? Is it time the television was switched off?

I was astonished to find how few opinions I had about children's behaviour when mine came along. I couldn't decide whether it mattered that they eat their meals quietly, finish their first course before their second, or ask to get down from the table. Admiringly, I would read the testimonies of parents and experts who had made their minds up on a range of diverse issues. But as fast as I constructed strategies to help me guide my offspring's behaviour, I was forced to dismantle them in the light of experience.

For instance, I defy any parent to have a pre-arranged position on the question of bath salts in the herbaceous border. When I spotted Frances, then four, sprinkling purple powder over the annuals, I reacted instantly. 'Stop that, please. It's not what you're supposed to do with bath salts.'

That would have been it, except that I caught a glimpse of her disappointed face as she sloped indoors. I reflected - what did it really matter to me? The salts would probably do more damage to her skin than the plants. 'I'm sorry. I've changed my mind,' I said. 'Carry on if you want to.' She was overjoyed, and I felt that any damage to the winter foliage was probably worth it.

I worry simultaneously about being under-involved and over-controlling. I often find myself standing, open- mouthed, with no strategy to offer at all. Frances has now turned six and a half and is shedding old behaviour patterns as swiftly as her teeth. I can't keep up with her. According to developmental theory, she's in her first adolescence and is sensitive to personal affronts she would not have noticed six months ago.

A minor misunderstanding resulted in her refusing to eat Sunday lunch with us this week. This was virgin territory, and I turned to my husband for advice. 'Should I insist she come in and eat? Should I keep the plate of food for her tea?' We decided on a neutral stance, and eventually she returned to the fold, ate the long-stagnant meal of her own accord and initiated a 'making-up' ritual by telling us a series of startlingly unfunny jokes. We all rolled around with relief and glee.

Perhaps these are the moments to make the most of: the unplanned cuddles and spontaneous closeness. Good times ought to be the foundation of good discipline. Self-discipline emerges when a child is given the chance to feel wanted, to be effective, to make up her own mind, and to make amends.

It's common, when faced with a truculent child, to blame ourselves, to imagine we are getting it all wrong. We suppose that our children are more badly dragged-up than all the rest. In desperation, we consult the childcare gurus - if only I had handled this more firmly, if only I had been more lenient in that situation . . . We imagine we can avoid the feelings of mutual rejection and inner failure.

But discipline is not merely a matter of toughening up, despite what John Patten would have us believe. It is not possible to go back to the days when discipline meant cold-blooded punishment - a wearisome but essential parental duty to be performed in high seriousness, separate from real life.

The modern child is not prepared to wait until his father, mother or other designated authority figure gets home. In reality, children learn discipline from every aspect of upbringing, by observing our decisions, testing our strength and flexing their moral muscles.

I have come to think it's OK not to have all the answers. Children are used to coping with contradictions, and there will be contradictions in the sanest of households. I no longer believe disaster will ensue just because my husband and I disagree on disciplinary detail. I have stopped pretending to be consistent when I am full of doubt. I have given up trying to control my children before they control me.

The Biro marks washed out of my loose covers with remarkable ease. I turned to Alice to express my incomprehension at what she had done, but her face was already full of trepidation and remorse. Her moral sense was alive and well, and she did not need words to tell her I was upset. She came to me for a hug, and sobbed her heart out.