My two daughters aged 10 and 11 watched their little brother being born at home. However, we talked at length before hand about how mommy would be in great pain and probably look (and sound) a little crazy, but that the whole process has such a precious end and it is all over relatively quickly, and that neither daddy or I were afraid so they didn't need to be either. I also told them that it was entirely up to them if they stayed or left if they decided they didn't want to be there at any point. I also told them that nearer the time I may decide I don't want anyone there and they wouldn't be called in. They and their little brother (only 2 so no question of him being there anyway) went round to a friends house and my husband called our daughters just as I was getting close to pushing. They came in and stood in the doorway and watched as he was born, then they left to tell our friends the news (they lived right across the street) then they came back about an hour later when we were all cleaned up and I was tucked in my own bed. They truly love that they got to experience it. (and I even managed a smile at them through the last bit which was a precious moment of encouragement). I do think that it made all the difference to me to know that they would only be there at the end and wouldn't have to watch me in pain for hours. So having a good friend so close was a blessing in itself. It is worth mentioning to that my older son was born in hospital as they waited in the room next door and afterwards both said they wished they had been there. (9and 10 at the time).
I haven't had time (or need) to decide if I would want/allow my son to be there. First thought is probably not, but that is more from his personality than anything.
Hopefully(?) that may be helpful.
All the best for whatever you decide!