my daughter is going to be six next month and wants a party at home for a few of her friends. i have a big garden so would plan to use that. However if it rains, we'll need to bring it inside. At six, would you expect the parents to be staying, or dropping off and coming back? All parties she's been to have been at a place (gym, soft play, country park and so on) so in that instance i would expect parent to stay, but what abut a party at home?
going on friends they drop the children off and let them get on with it, if its indoors, i guess if there was a tipple on offer for the adults they might hang around a while.
When my ones were young they just had a birthday tea at home with about six of their friends. They were all dropped off and picked up again afterwards.
Bouncy castle good idea, always goes down well but needs an adult to watch it all the time. From experience know that children get very excited and start doing silly things like jumping on each other!