First, recognize that the newbie will affect the “oldbie.” Don’t minimize the challenge s/he faces. It’s competition for attention and energy and love. We have two cats. Our older cat is shorthaired; she doesn’t need to be brushed. The newbie, now here several years, has extremely long hair. He definitely needs to be brushed. When my wife brushes him at night, our older, shorthaired cat, jumps off the bed for her turn at brushing.
So, sibling rivalry exists everywhere. Before your new child comes, tell your “old” child what is happening. There are many books, pamphlets, and videos. If your doctor doesn’t have them, check with your local children’s librarian. Have him or her be part of the process. Have her or him feel the expanding tummy and listen to the coming sibling.
Gauge your “old” child’s level of understanding so that you can talk to her or him appropriately. Tell her or him of the changes that can be expected. See if he or she is willing to talk about feelings. When our son was born, our daughter remarked, “Can’t we take him back to the hospital and go out for pizza the way we used to?”
Find a replacement or transition toy for her or him. We got our daughter a doll bigger than she was. She played with it, kicked it around for a while, and then got bored when she found that her real brother was a better toy! If possible, give the older child her or his space, such as a room or a corner that can be made their own.
This is very important: you should watch out for reactive behavior. One client of mine, a five year old, has begun to urinate around the house, in effect “marking territory.” Other kids may start to develop symptoms, including diarrhea or stomach problems. If this happens, take your child and your family to a therapist familiar with these problems.
Give your older child her or his special time, with you or your partner. Make sure you do! Tell them, too, that they’re the older sibling and they are special and their younger sib is partly their responsibility.
If none of this works, again, go to your therapist!