I think it depends on the birth, and obviously you won't know that until its too late! I wouldn't have wanted a child at my first baby's birth, but it would have been fine to have a child at my baby's birth. I agree with pp's that if you are going to do it, make sure you explain to your DS what he might see - eg blood, poo, his Mummy making funny noises, people doing strange things to you etc.

Given that you can't be sure what is going to happen with your birth, I would probably choose not to have my children there for the delivery, but if they could be there within 30 minutes of birth that would be perfect.