InternationalFlight - take a deep breath!! It wont be as bad as you imagine it will
The parents around here all seemed uber loaded and competitive until I got to know them - then realised most of them are actually quite nice, quite normal people, living in quite 'normal' houses (some are 'renovating' too ). Most of them do hire a hall and entertainment, but it's not to be competitive or because they are loaded - it's simply because they cannot be arsed doing it themselves and would rather pay - last year they were in awe of us having LO's party at home. This year we are hiring a hall/entertainer, but only because LO really, really wants to have one 'like the others', so as we can, we are... even though I think after the event she will look back and prefer the party she had last year (kids! LOL).
I would definitely go with the Pirate Party in the back garden, treasure hunt, flags/parrots/treasure they can selotape to the climbing frame, water bombs etc (Put on the invites that the kids need to bring a change of clothes!!).
Personally (and especially if you aren't socially confident), taking half a dozen kids out anywhere, is daunting, let alone kids you don't know (so have no idea what their behaviour will be like!!). I'd be worried about one of them running off if I didn't already know them .
Have a few games up your sleeve (pass the parcel (we put a small packet of evil Haribo between each layer and a small pressie inside), pin the parrot on the pirate (get DS to help make the pirate), treasure hunt etc. But, to be honest, they mostly want to be left alone to play!
Buy pirate paper plates, cups & napkins - squash, cocktail sausages, crisps, cherry tomatoes, grapes, a few small sammies (or as sayithowitis said rolls to make themselves)and some ice cream - job done Oh and if the budget can stretch to it, some wine/beer for the adults
Personally I think you should do a party bag, they can be very cheap, but kids love them. Even if you just put a balloon, chocolate coins and a small 50p gift in it with a piece of the cake, kids love to take them home.
Also, if you are happy to have the parents leave, put it on the invite so they know that!! Time: 11 - 1pm (please feel free to drop and run!!). Some parents will stay anyway - put them to work!