With our first homebirth (UC), my oldest was almost 3 and actually slept through the whole thing. It was great! Dh woke him up about 5 minutes after the baby was born.
With our second, my oldest was 5 and my youngest was 2. He played the computer a lot during the labor and she watched some. She ended up taking a nap and then waking up right around the time things got really difficult (which is also when I called dh home from work, I was home alone with the kids before this point). Dh went back and forth between us since I was just in the bathroom next to the computer area. He let them come in a minute or two after the baby came.
With our third, it was the middle of the night. I was SOOO excited about that because I thought I'd get to labor in peace. My 4yo woke up after an hour, then my 2yo woke up, by the time I hit transition around 3 1/2 hours in, my 7yo was awake as well. At this point, I woke dh up and hit the shower alone. He came in for the pushing and then let the kids in after a few minutes.
With our fifth, it was all during the day. LOOOOOONG day. For the first several hours, things were great. I made breakfast and lunch and worked through contractions. The kids had no idea I was in labor. Dh sent them into their room (shared) when things got difficult so I could concentrate and they wouldn't worry. My 2yo was out though. She is a total Daddy's girl. She was not impressed that I was in heavy labor, but she didn't cry or anything. I always prefer seclusion when transition hits, so I went for the shower eventually. I called dh in when I was pushing, and he asked Dd2 if she wanted to come in. She refused.
She is the first one we've invited in. After the baby was born, I moved across the hall to our room and she came in for a few minutes. Once I was dressed, dh called the big kids and they were shocked that the baby was here.
I don't know that I'll ever let my kids watch a birth, but having them around in early labor doesn't really bother me. I don't like ANYONE around me in transition, so I go for the smallest room in the house generally. I thought dh would be bothered by having to keep track of Dd2 during labor, but he said he really liked having her around. He doesn't particularly like labor and gets really anxious, so having something to keep him busy was a benefit. Baby #5's labor was my least favorite of our homebirths beceause it hurt SO MUCH for so long, but dh said it was his favorite. Which is awesome. If he can have such a good experience while I'm having a crappy one, that is encouraging to me.
For baby #6, my kids will be 11 (maybe 12, it's due the day before #1's birthday), 9, 6 1/2, 4 1/2, and 2 1/2. I imagine if it's daytime, we'll do the same as last time and send the big kids in the other room to play when things get tough.