From the other posts, it seems clear that whether or not your older (toddler) child is present really depends on the child. My wife wanted me to respond as her memory was pretty much on the hypno-imagery stuff and the pushing later on while I was the one moving around with dd, birth asst., & the midwife throughout. I hope our experience helps illustrate our opening statement/observation.
Our dd was 2.5 yrs old when ds was born at home. We brought her to the hypnobirthing sessions throughout the pregnancy and we talked about Mama making noise and even the fact that there'd be blood (her question, not ours), etc. We emphasized the normality of it all which seemed to enable her to treat it nonchalantly. We did have our best friends all set to come over but Mama began labor in the evening (right when we were sitting down to play dreidel -- fourth night of Hanukkah, surprise!) and then we never got around to calling on them. We had a doula/birthing assistant who had done all the hypno stuff with Mama and dd. She came over right away and our midwife came over a few hours later. Mama was really digging her "special place" and dd spent the first few hours of labor stroking mama's arm and "helping" out (did some puzzles at one point when she got bored, then came back).
When we moved to the bedroom, dd came along but she curled up at the foot of the bed and slept while mama did some serious groaning and pushing work. She woke up just in time to greet her new baby brother and man, was she ever stoked! It was the calmest, quietest experience (well, from the "other" side of things, mama did all the hard work of course) overall and our dd really was such a part of things she had a great experience too. IN fact when we brought her brother to temple for the first time, she made sure everyone knew she saw him first when he was born. (most people didn't get that but we got a kick out of it).
All the best with your homebirths,
Dov & TeachinMama