Is this really bonkers?
DD1 (4) is having a birthday party next month. She wants to have her party at home, like she always has had in the past. Attempts to encourage her to consider a party at an alternative venue have fallen on deaf ears. However, we've just sat down to write the list of invitees and what started with her "must-have" list (comprising 5 kids), we've added the reciprocal invites and the names of children we know whom it would be weird not to invite as they've always come before and the list now stands at 19 (!) children.
Previous years we've invited around 10 kids and it's been a bit of a free for all with siblings and usually both parents, but this year it looks like we just won't have the space 
We're in a small three bed semi with a decent sized garden.
So, is there a way I can make this manageable? How can I tactfully suggest that parents drop and go where possible?
Anyone used to doing massive children's parties at home with some handy hints for activities (previous years they've just been tearing around the garden in their pants playing, but I sense an expectation of more formal activities now they're at school), seating arrangements etc, please share your wisdom!
I'm keen to go ahead but need a bit of "hey, it's just an afternoon" kind of encouragement!