When our second son was born, I had my five-year old in the room, and it was wonderful. I had my sister bring him in and stay with him, knowing she was there just for him. He came in towards the end and knew that he could be there or leave, be with me at any time during my labor or not. I had shown him some birth videos beforehand and talked with him extensively about how the mommy was feeling some pain but it wasn't going to hurt for long and it was okay because his brother was going to come out that way. He watched the whole thing and gave me strength. I think it's really important to have someone else there for the child, though, so you or your partner don't feel like you have to take care of them. I have sweet pictures of him helping me breathe through contractions. He felt very close to his brother. When I started pushing and my water broke, he said, "YUCK!" We still laugh about that. And after everything, he whispered to me, "You're not the bravest mommy." He was thrilled to be a big brother, and fascinated and excited to be there to see his baby. It was a natural labor, NO EPIDURAL. There was no trauma, there were absolutely no regrets about him being there.
When their sister was born, the boys were nine and four. They were both there and it was really amazing and beautiful. They were both rubbing my back and helping me breathe deeply. They were right there to kiss their baby sister. They felt like an important part of the process. Once again, it was natural, peaceful, and amazing. There was no trauma. The posts recommending epidurals to spare the child from seeing pain or saving them the "trauma" of watching birth are missing part of being alive! Showing them that it's natural will help them in so many areas of their lives. Our bodies are built just right, to make the baby, to bring the baby out. There's nothing traumatizing or disturbing about it. Your attitude will matter a lot here, too.
I love the idea of having little ones see how normal and natural birth is, respecting what the body can do, seeing their mom in all her glory bringing life into the world. Seeing that something painful can bring something beautiful. Seeing someone work really hard for something important and getting the prize at the end. There's so much to share with them.
I would make sure it's what he wants, talk with him and show him videos before to make sure he understands what will be going on, and explain in very clear terms that you might be making noise, there will be blood, that you'll have to work very hard, and that it's all going to be okay.
Best of luck to you! What a lucky boy to have such a thoughtful mom! Bottom line, birth is a natural process and a wonderful way to bring life into the world. If your son is interested in being there, it's a wonderful gift you can give to have him see what you can do. To be there for his baby being born.