Here are some ideas to help with the second child / big brother or big sister transition.
When you share the baby news with your current child during pregnancy, it can be helpful to frame it as adding to your family. Let your child know how much you and your partner wanted a family, and you were so happy to have him or her. Now you and your partner are excited again to add to your family. Express some of the complex feelings s/he may be experiencing: I imagine you may feel happy, sad, excited, angry, etc. Name whatever emotions s/he seem to be sharing.
Talk with your child about the logistics of what will happen when you are in the hospital: who s/he will stay with; when s/he will come visit you and meet the new baby, etc.
Make sure to have some solo time with your older child in the hospital when the baby is in someone else’s arms or sleeping in the newborn crib. Have him or her sit or lie with you and check in together.
When you get home, you won’t be able to do everything s/he wants you to do during your birth recovery, but you can do slow paced things each day with your older child like reading books or cuddling.
Once you are more mobile, have special outings with just your older child. When you are out remind them that only s/he can eat pizza or go on the big slide, etc., not the baby.
Tell him how much you love him or her and how grateful you are that s/he will always be your first baby, and how special it is that now s/he is a big sister or brother.
Use positive reinforcement for each time s/he does something helpful and kind with the new baby.
Expect some regression or acting behaviors. It's natural and this behavior is a young child's way of processing such a big family transition.
Books for kids:
Daniel Tiger: The Baby is Here
by Angela C. Santomero and Jason Fruchter
I am a Big Sister or I am a Big Brother
by Caroline Jayne Church
Books for parents:
Siblings without Rivalry
by Adele Faber and Elaine Mazlish