Well, dd's 3rd birthday party is next week and this is what we've got planned (sounds similar, about 30-odd adults, 6 older children, 10 3yr olds (so far!)) -
4pm - 5pm, let them run amok on assortment of stuff - bouncy castle, paddling pool filled with balls, seesaw, slide, tunnel and tent, mini-trampolene (surrounded by crashmats), plus tables set up for colouring in (for those who don't want a rest/don't like bouncy castles)using printouts from various telly sites/free online colouring pages and Asda's smartprice coloured pencils (so not too expensive or messy!).
5pm-5.15pm, party games - NOT my idea, I hasten to add - dd has gone mad for the idea of musical chairs/bumps/statues, so we will be doing some version of them (quite like the sound of the musical islands game mentioned on the Pirate Party thread!), plus we have a game involving sheets of big bubble wrap - split the kids into teams, assign 1 adult/older child to each team to manage them, then relay race to see which team bursts all the bubbles first.
5.15pm-5.30pm action songs/rhymes & dancing - most of dd's friends go to nursery so they all do this kind of thing
5.30pm-6pm - throw pizza and icecream in their general direction
6pm - cake, candles, party bags and home!
Of course, it's highly likely they'll be so excited by the bouncy castle that they won't want any other entertainment (suits me, quite frankly!) but I have it all prepared just in case....