If you have other children, you'll need to plan carefully how and when to tell them about the new baby. A child who is four or older should be told as soon as you start telling friends and relatives. If your child is younger than four when you first become pregnant, you can wait awhile before telling him. When he's this young, he's still very self-centered and may have difficulty understanding an abstract concept like an unborn baby. But once you start furnishing the nursery, he should be told what's going on.
Picture books can be helpful with very young children too.
Even if he doesn't ask questions, start talking to your child about the baby by the last few months of pregnancy. If your hospital offers a sibling preparation class, take him so that he can see where the baby will be born and where he may visit you. Point out other newborns and their older siblings, and tell him he's going to be a big brother soon. But reassure your child that you will love him just as much, and help him understand the positive side of having a baby sibling. If your child is between two and three, he's still extremely attached to you and doesn't yet understand the concept of sharing time, possessions, or your affection with anyone else.