• Prepare your child for the new arrival. About three or four months before the new baby is due, tell your child, truthfully and directly, about the coming birth. This is a good time because he can see some evidence of what you're talking about; your tummy will be big enough that the concept of a baby in there won't seem too abstract to him, and he'll be able to feel it moving and kicking. Plus, you won't be telling him the news so early that he'll be likely to forget all about it or get antsy waiting for the impending birth.

Describe the changes that will take place in your household once the baby arrives and how they may affect him, positively or not. Encourage him to ask questions and to tell you how he feels. Assure him that none of this will affect how much you love him. "Some kids require more reassurance than others, though," says Dr. Elias, "so don't assume that one, two, or even three explanations will always do the job."

• Let your toddler play decorator. Invite your child to help you set up the baby's room and pick out furniture or supplies. If you need to change his routine (move him into a different bedroom, for instance, or graduate him from a crib to a bed), do it at least a couple of months before the baby's arrival so he doesn't feel displaced. You'll also want to resolve — or simply drop, for the time being — toilet training or battles over food, since children are known to regress in these areas when a new sibling arrives.

• Explain what will happen once you go into labor. About two weeks before your due date, prepare your child for your upcoming absence. Discuss the arrangements as clearly as you can so you can dispel any fears and doubts. Though you'll likely be at the hospital for only a couple of days, he'll probably be distressed by the upheaval. If a relative, friend, or babysitter is going to stay with him, you might want to ask that person to spend a night in your home a week or two in advance. If possible, have your child come to the hospital after the birth so he feels that he's an essential part of your new larger family right from the start. Some families even have birthday parties with a cake and a present for the child from the newborn.

Once the baby's home:

• Involve your toddler in baby duty. Let your firstborn help out — he may surprise you with how much he can do. When you bathe the baby, he can hold the towels or help soap the baby's legs. When you're out for a walk, let him push the stroller (with you lending additional strength and navigation, of course). If your child begs to hold the baby but you don't think he's strong enough, have him sit in a chair with pillows on either side of him, then prop the baby in his lap (remaining nearby yourself to make sure all is well).

"Ask your toddler for advice and help," suggests Dr. Elias, "such as 'What do you think the baby would like to wear?' or 'Do you want to help me tell the story?'" Younger children often have a natural flair for entertainment — singing, dancing, or just making faces. And a baby is an appreciative audience. Not only will your toddler enjoy the attention, he's also likely to take pride in being able to make the baby smile. Point out how much the baby likes him, especially if other grownups are present. "Look at how she smiles for her big brother!" Like grownups, children find it easier to like, or at least accept, people who like them. You may also want to use books to help your toddler adjust. Joanna Cole's gender-specific I'm a Big Sister and I'm a Big Brother are good places to start.

If your toddler doesn't want to help, though, don't push it. Many children simply prefer to ignore their tiny siblings — at least for as long as they can. So don't force your child to play a greater role than he wants to. He may come around in time, but you could easily create additional resentment by insisting that he help.

• Provide plenty of "Mom" time. It's natural for your child to feel jealous. Suddenly he's got to share you with someone who requires an extraordinary amount of your time and attention. Rather than scolding him, acknowledge his feelings. "You wish I wouldn't spend so much time with the baby," you might say, so he knows you understand his point of view. Take some time each day to do something just with him, even if it's just a few minutes of drawing or building with blocks.

If your baby goes to sleep earlier in the evening than your older child, designate an hour or two as "big kid time" and use it to read, play games, or look at family albums together. Show your child pictures of himself as a baby, and tell him that he needed lots of special care, too. This may help him understand why you now need to spend so much time with the baby. Point out the perks of being a big kid — how he walks, talks, dresses, and plays by himself. If this makes him patronizingly tolerant toward the baby, consider it progress.

• Be prepared for aggression. Young children who feel jealous commonly act on those feelings. Don't be surprised if your toddler hits or throws something at his new sibling; if he's old enough, he might try to make it look like an accident. While your little one's aggression toward your other beloved isn't easy to witness, it's normal. But do take steps to prevent him from hurting the baby. When you're alone with your older child, encourage him to express his feelings of jealousy and anger. Tell him it's natural that he feels this way and it doesn't mean he's bad. But make it clear that acting on those feelings is not okay.

If he is aggressive, intervene right away. Don't humiliate him or punish him physically; doing so may prompt him to take revenge on the baby later. But tell him plainly that his behavior is unacceptable: Say, "It's not okay to hurt the baby. She hasn't tried to hurt you, and you're much stronger than she is." Give him a time-out to think about his behavior. For a couple of weeks after an aggressive act, don't leave your toddler alone with the baby, but try to be subtle about this, as you don't want him to feel that you don't trust him. Even if your older child is generally affectionate, take all the obvious precautions — remove sharp objects while you're out of the room, and don't leave him in charge of the baby carriage.

• Try not to foster competition. Resist any and all temptations to compare your children. The classic "Why can't you be more like your sister?" is bound to hurt feelings. Instead, emphasize each child's strengths separately with positive feedback, and praise and reward them together whenever possible: "Wow! Nobody spilled their milk tonight!"

• Help them work together. Look for opportunities to get your kids into situations that require cooperation — any activity in which they share a goal will work. They can put away their toys together, for instance, or help each other get ready for the park. And when your younger child needs help — putting on her sweater or retrieving a favorite book — your older child might be able to help instead of you.

Think of noncompetitive games and other activities that will allow your children to shine as individuals while enjoying each other's company. Lots of imaginative games will let them play different yet supporting roles: setting up a pretend store, making a fort with couch pillows, having one child pretend he's an explorer while the other plays a wild animal he's befriended. When little ones get quarrelsome, a good strategy is to engross them in activities that naturally lend themselves to sharing. Finger paints and Play-Doh are too abundant and amorphous for one child to claim as his own, and you may even witness a cooperative creative endeavor, if only briefly.

• Teach them to resolve conflicts on their own. As your children get older, your goal is to have them settle their own conflicts as much as possible. While you can't realistically expect this from toddlers or preschoolers, you can set the stage by encouraging your children to listen to one another and find solutions on their own. With a toddler and baby that may mean going to separate corners of the room and playing by themselves if they can't stop fighting over a toy. It won't be long before they miss each other or get curious about what the other one is doing. Be sure to praise your children lavishly any time they work things out themselves.

• Divide and conquer. Children tend to go through periods in which they get along well, and periods when they seem to fight all day. When your family's in one of the grumpy phases, sometimes splitting up into child/parent pairs can ease the tension. One child gets a "Mommy day" and the other a "Daddy day." If you're a single parent, you might want to enlist a friend or relative to help you give each child some private time.