We have 4 kids, and our kids have always been with us. The youngest were always under 2 when the baby came.
When I had my 2nd, I went into labor at 11pm. Our almost 2yo, woke up at about 4am. I'm sure she heard us. She lived in a tiny apartment. She was happy to watch me in the pool, walk around, moan, make food with me, eat. Whatever. We planned for a friend to come over to take care of her. At around 8am, we called for her to come over. It was helpful having someone there just for her. When I had my 3rd, we were in Hawaii, and I went into labor at about 8pm. The kids fell asleep on the floor in my room because they wanted to stay up to see the baby. DH moved them later. And woke up our oldest when the baby was coming so she could be there. But we left our 2yo to sleep. We didn't have anyone there for the kids and it worked out this time because they were asleep.
This time we'll have a 3yo, 5yo, 7yo, and 9yo when this baby comes. I am planning on being in my parents home for this birth (weird!), and so my parents will help with the kids tons.
I think it is useful to have someone there, but one thing about homebirth that is awesome is being able to let the kids see that labor and birth are normal events in life. I don't like the idea of separating them from me (making them leave the house) - and I do like them to be able to see the baby as soon as possible after the birth, or see the birth if they want to. I don't push it either way. We have never had a problem with any of the kids being jealous of the new baby at all. I am sure this is not solely because of the homebirth, but I do think keeping them involved has surely helped. I have so many friends that have hospital births where the siblings are so jealous of the baby and are even mean to the new baby. I have never witnessed that in our home, thus far. I don't want my kids to think that I can't handle them being around me during labor so much that they have to leave their home. There are times when I might not want a child around, but my husband always recognizes this and takes action so the child doesn't have hurt feelings. During my 2nd labor, our almost 2yo was being really annoying to me, asking me questions every 2 seconds, and telling me she was hungry (I was mad about that, but she is used to coming to me for stuff like that and not the caregiver I provided for her), and we had to shut the bedroom door for a while so she could be distracted, and I could concentrate. But for the most part she was very agreeable to have around.
That is just me - and my opinion, and experiences. To each her own of course!! I like having my kids around. I like them to see labor and birth, if they want to pay attention. They say funny things (why is it taking so long?? eww, thats gross!! maybe your belly won't be so fat anymore!!), and I like them to feel a part of the excitement of what is happening. I want to present birth as normal, and that they can be as much a part of it if they want to. But yes, if I want them to leave the room, that is what I want. I just don't want them far!! I like having a care provider for them wherever I am giving birth. Just make sure, if you do it that way, that the person knows what they are there for - the child(ren) and not to watch the birth.