My son was a month shy of turning 6 when we had his sister. And yes, he was present in the delivery room.
We had DD at a teaching hospital, so the OB delivering her unfortunately was not the doctor I had seen up to that point. If I had known I could request it differently, I would have because she was not keen on having him there. The regular doc, Dr.M was a big fan of family involvement and was just wonderful. He viewed childbirth as a natural occurence, not some medical procedure, does that make sense?? He was very much granola........and we all loved him. Still do.
DS accompanied me on most of my check ups, was present during ultrasound, and Dr.M had the teaching library loan me some wonderful videos and books on childbirth to share with DS. He knew exactly how things would happen, that mommy might cry or scream, there would be some blood or other icky messes and that if he wanted to leave the room he could.
We had a friend with us for delivery who could stay with him if need be.
DS held my hand as I panted, he rubbed my back while I was on the birthing ball, he comforted me with words and was just wonderful. He would tell me "It's okay, mommy, it will be all right" if I started to cry from the pain. (No epidural.)
When he wasn't comforting, he was playing a game on DH's laptop.
The delivering OB was a real witch, didn't care for her at all. She was angry about us having DS along, wouldn't allow us to video, didn't want our friend in the room, etc.....
Thank goodness Dr.M was working in the ER and saw our name come up on a computer screen!
The witch had sent DS and friend out in the hallway against our protests, saying they couldn't be in there.
Dr.M ran up three flights of stairs when he saw that I was in, scooped up DS into his arms, ran into our room, and threw DS onto his shoulders so he could see "his baby" being born.
DS remembers feeling a sense of wonder and excitement at that moment, remembers her first cry, how tiny and pretty she was. He has no bad memories of the birth.
We did video later in my room and the excitement and love in his voice is tangible as he talks about how "I love my mommy, and my new baby sister, and my daddy who is taping this".
I would have them in the room again in a heartbeat if we had another baby.
I should add that when DS was born, my 14 year old brother videotaped it for us and he says it was a wonderful experience. Again, you hear absolute wonder in his voice on the tape. That was 12 years ago!