Hello, your excitement is understandable, since children at this age still have many fears associated with loneliness and separation from the mother. Therefore, it is necessary to prepare the child for the second birth, this will reduce anxiety and help the child to adapt to the idea that a baby will appear in the family.
It is best to say this at a time when the stomach starts to be rounded, as it is very tiring to wait too long for children. You can read to the child the work of fairy tale therapist Tatiana Zinkevich-Yevstigneeva "The Tale of the Bear", Dina Trushina "The Tale of the eldest daughter." O. V. Khukhlaeva, O. E. Khukhlaeva “The Tale of a Doggie named Tobik”. And you can yourself come up with a story that will reflect a similar situation. That is, the eldest child will be the main character, and the second character will be the baby.
The main task of all these tales is to help the child cope with anxiety caused by the birth of a baby in the family. Tell your child about what is happening to you, let's touch the tummy, take it on the ultrasound, show photos where it was also so small. Let him help you when choosing toys and clothes for the baby, it may be worth visiting friends and acquaintances where there is already a child.
Use play therapy, you can buy a set of dolls - a pregnant mother and baby, draw pictures for the future baby, choose songs and music. Explain that with the birth of a baby, life in your family will change, but you will still love and pay attention to it.