H.D.
With that many people why not go to a bounce house place (or depending on the weather) rent a couple of bounce houses and throw the party at your own home? You could ask for your family to help bring potluck type dishes for the adults and you could supply the simple foods 5 year olds like such as corn dogs or pizza. Another idea is to look into your local rec center for a swim party and they may have a room large enough to accomodate your large group for a get together of cake and ice-cream at the end. One last idea i'm thinking of could be to hire a make-up artist and balloon twister and just entertain everyone at your local church or near by park and only serve cake. I'm sure not all the adults will be into games so you could get a pull string pinata for the kiddos and hand them a goody bag to grab whatever falls out as their treat to take home.