My son is 41 and he has never given me a Mother's Day card, and never will. But that's OK, because while he may be my son, I'm not his mother - I'm his stepmother, and that's a different thing entirely.

Nevertheless, when Mother's Day rolls up in ten days' time, the absence of cards will be a source of hurt and even conflict for many stepmothers. More than a few - many stepmothers try so hard to make up for what led them to be there in the first place - will think that they have all the work with little reward or recognition.

Most events and anniversaries have the potential to cause immense upset and sometimes quarrels in a step-family because they highlight the fact that the family exists on the foundation of another's dissolution. Someone has to have died or some relationship has to have come apart for it to be there at all.

Step-families come with so much baggage and unfinished business. Adults may still be simmering with anger and feelings of rejection; children may be struggling with fears that the split was somehow their fault. A new relationship will be seen by the parent concerned as a gift, a joy, a new beginning. The children, however, will see it as an ending; the final nail in the coffin of their hopes that Mum and Dad might get back together again.

However quarrelsome and unpleasant the relationship might have become, separation, divorce and re-partnering are always adult solutions to adult problems. Children would far rather you patched up and stayed together.

This is why step-families are such volatile things, with complex and often contradictory emotions flying around. You, as the parent or step-parent, may think that it's all settled and a done deal, that it makes sense to be happy about the new scenario. But as far as the kids are concerned, who asked them, and what's to celebrate? And so, like other anniversaries, Mother's Day and Father's Day have the potential to upset everyone.

So the card thing suddenly achieves disproportionate significance. Parents, whether living with their children or seeing them on contact visits, may expect a card and be hurt if one is not forthcoming. They may also assume that a card will be forthcoming to a partner they feel is trying their best and be hurt on their behalf, and furious at the perceived slight if it isn't.

Or one or both of them may be furious if a child gives a card to a parent that their ex feels doesn't deserve one. The child might actually be doing it more as a way of asking for attention than as a recognition of a job well done, but the other parent may not see this. Children may give cards to a parent who has done well by them but who did a lousy job of being a partner - again, the result may be tension and upset on the part of the other parent.

Children may not give a card to a parent who has struggled and strived to do their best in a difficult situation. The child may be hitting out at the situation, or delivering a sideswipe really felt towards the non-resident parent whom they dare not upset in case they walk away. (Kids tend to blame the parent they feel most secure with rather than the one to whom they feel anger or resentment.) Or they simply may not do it because no one has reminded them to do so.

Above all, many children see it as neither necessary nor appropriate to give a Mother's or Father's Day card to a step-parent, however well they are doing the job of parenting, however much they may be loved or however much they deserve it. Even if they are the only mother or father figure these children have in their lives. The reason may be twofold. One is that a step-parent isn't a mum or a dad. I'm not my stepson's mother - never have been, never will be. I am a significant other, I'm the third person who brought him up in partnership with his mother and father. But children have one mum and one dad, and they don't accept substitutes. The trick to being a good step-parent is not to try to be a stand-in but to see yourself as an extra - something different, something supplementary, something giving added value. Accepting or demanding or even just expecting to be given the name of Mum or Dad crosses boundaries.

Perhaps the answer is to encourage a Stepmother and Stepfather's Day - a day when the many families that come in all shapes and sizes could celebrate and show appreciation of each other. Step-families are becoming more common - by 2010 the traditional “two people who marry, have kids and live together for the rest of their lives” family will no longer be the norm.

In my experience it's not the fact of separating and re-forming that damages children, but how you do it. Many stepfamilies are places in which children thrive and adults get a second chance to parent better. But if we are to support families to understand why it may be hard and what you have to do to make it easier, a first step would be simply to acknowledge the new reality. Stepfamilies exist and step-parents often do their best.

Until we get such a day, it's fair to say that there will continue to be a lot of wistful stepmothers out there on March 2. But not me. My badge, my gold star and bunch of ribbons came one afternoon two years ago when my son and his lovely wife announced that I was to be a grandmother - not a step-grandmother but a full one. Grannies get handmade cards, too.

Suzie Hayman is a counsellor, accredited parenting educator and agony aunt. Her latest book, Teach Yourself Successful Step-parenting, Hodder Education, £8.99, is out next week

Dos and don'ts on Mother's Day

If you're the stepmother, don't take it personally if the children choose not to send you a card. It's not about you.

If you're the parent, don't take offence if your children give their step-parent a card.

Rather than dropping hints and then feeling hurt, make it the subject of a family discussion.

Give children a chance to explore what they feel about it, explain your own emotions and what the other parent may be feeling.

Give children the right to make their own decisions with no apparent or hidden pressure.

Look after yourself. If you're getting the rewards elsewhere - from your partner and by awarding yourself points and treats - you won't feel deprived if no card is forthcoming.