Imagine, women readers, that your husband told you he had great news. That he was going to get a new wife and that she'd be company for you. That you could share all your things with her and help him look after her. And that of course he still loved you, in fact it's just because he loves you so much that he wants to get another wife!

(Male readers, kindly read the above with the roles reversed.) How would you feel? Shocked, no doubt, and disturbed. Well, according to the experts, this is pretty much how your toddler feels when you tell him he's about to have a new brother or sister.

And what's worse, he can't articulate his feelings. Or perhaps if he does protest, you tell him not to be silly - he'll have great fun with the new baby.

It can be quite tough on a small child to have his world upset by the arrival of a new baby. "You may find that you have to keep an extra eye on your two year old who wants to help by carrying or picking up the baby," writes Sandra Hardin Gookin in Parenting for Dummies (published by IDG), "while your eight year old suddenly seems to get angry at you for no apparent reason. Whatever the age of your children they may experience increased crying bouts, temper tantrums and regressions (such as bedwetting, acting like they can't feed themselves, wanting to be carried when they are fully capable of walking and so on).

"You may find that younger children actually try to take the baby out of your hands so they can crawl into your lap. These actions are signs that your children feel insecure and need your attention."

Anyone who has had a child go through a phase of intense jealousy over a newborn will tell you how upsetting it can be. In the States some maternity hospitals actually run sibling classes to introduce the idea to small kids. So it makes sense to ease the way as much as possible. And jealousy can happen at any age. There's a gap of nearly 10 years between my eldest and the next child, and he was thrilled with the new arrival; however, at Christmas, three months after the birth, he protested that the baby had got more presents than he had. This was blatantly untrue, but it made me realise that despite his maturity he felt a touch of displacement.

If you bear in mind that all the baby books warn that Dad can feel envious and left out, obviously a child of any age can feel affected.

If you expect your child to be a bit jealous and try to understand his feelings it makes it easier all round. Tell small children as much as you can, as simply as you can. You'd be surprised how much they take in. "When I was around three or four months pregnant I started pointing out families with two or more children in books and on television, so that Finbar would get the idea of having a new sibling," says Moira Byrne, whose son was three at the time.

"When Finbar was born his older brother spent the first three months trying to kill him. So I was determined to ease Finbar into the idea. I didn't actually tell him we were having a baby until around seven months because kids' understanding of time is very different from ours." When you tell him about the new arrival, don't say he'll be able to play with baby and share his toys, because he will have unrealistic expectations: when he dumps his tractor on the new baby's head or runs his car across her face he won't understand why you scream at him.

It's better to tell him that new babies do nothing but sleep and feed and occasionally cry. Show him pictures of himself as a newborn and explain to him that your new baby will look like that. You might let him feel the baby's kicks in mum's abdomen and explain that he's not ready to come out yet but that he'll be out soon. You can let older children join in the decisions on names, though he may be thrilled to think you could call the newborn Barney, or Dipsy, or Socky!

Treat his ideas with respect - you might consider one as a second name or as a pet name if it's not totally off the wall - but explain that you have the final decision. There are lots of children's books about new babies which can be helpful. "Some of them explain about mum going off to hospital and Gran coming to mind the other kids," says Grainne Halligan. "I found my son remembered these when the baby was born and they were a comfort to him. He knew there was room for two on my lap because it showed it in the book."

If your child is going to have to move out of his cot into a big bed, do this months before baby is born and don't say it is because of the baby or he may hate her for it.

Any major changes such as potty training, getting dressed on his own, starting playschool, changing minders etc are best done a couple of months beforehand. "If you suddenly pressurise him off breast or bottles, and out of nappies and into a big bed on his own, while this squeaky new baby sleeps in his cot, or worse still in your bed, wearing nappies and sucking contentedly on mum's breast or a bottle, you are heading for outright war," Moira Byrne says.

"I think this is where we went wrong with our first two."

If the new baby is imminent and you haven't weaned your older child off any of the above, don't do it now! Wait until the baby is a few months old, then gradually make the changes.

When your older child comes in to see mum after the new baby is born, make sure dad or a nurse is holding the baby. Mum's arms need to be free to cuddle the older child, who will have missed her while she was in hospital.

He will be intrigued to see what all the fuss was about - and amazed to see mum in her nightie in a strange place! Explain that she'll be home soon and glad to be back with him and the baby so she can read all his favourite stories or whatever, so that he knows that despite this bizarre happening life will go on as normal.

"Have a present ready from the baby to him. That will make him think she's not too bad," says Elizabeth Clarke. "Tell your family also that you'd like something tiny for the two children rather than just a present for the baby."

The good news is that with a lot of patient loving care towards older children - which can be a tall order when you're exhausted looking after a newborn - the new baby will soon be seen as an integral part of the family, and the older sibling will no longer consider sending him back!