OK. This is what we had for joint birthday party for DS (3) and DD (1). I'm assuming that everyone in the whole world has those small colured plastic bowls from IKEA that cost about £1 for 10 or whatever and the flower shaped plates and the beakers (much cheaper than disposables).
Bowls of organix puffs and twigletts (altho hula hoops have also appeal and can be eaten off fingers)
Bowls of cherry tomatoes; cucumber batons; carrot sticks; grapes.
cheese and pineapple (fresh, I'm posh) on cocktail sticks stuck into a potato covered in foil (thought children might wet themselves they were so excited by this). Good poking potential with cocktail sticks also, much appreciated by 3 year old boys.
Few sandwiches: grated cheese and marmite; tuna mayo. These tend not to get eaten, TBH!
Mini sausages - I work right next to a sausage shop and they make up batches of cocktail ones on 48 hours notice. Think of the maximum anyone can eat and double it - hugely popular with parent attendees (and more cocktail stick fun!). If I'm feeling fancy I drizzle them with runny honey before cooking.
Chocolate crispy cakes (never eat them the rest of the time). If you do this sort of thing you have to do it properly - I have an unbelievable recipe (Annabel Karmel of all people) that includes melted mars bars and then when set in a tray you make a chocolate top to it as well - brilliant.
Biscuits in number of birthday boy (have great number cutters from Urchin I think - about £10 but we are going to get lots of use out of them). Cover in different coloured glace icing and different sorts of sprinkles (DS helped with all this on his last birthday). I put these in party bag. Also nice to send in to nursery school on birthday itself.
Cake (last year DH made a Thomas the Tank engine cake but usually we do a number one - you can rent tins really cheaply - couple of quid)
I also put out some biscuits next to the kettle for parents plus tea, coffee milk and sugar on the side. Then offer wine (or indeed champagne) at the end when cake is cut.
We always have a bouncy castle (loads cheaper than an entertainer, actually) so food definitely AFTER bouncing. No one has been sick so far (although DD was so over excited last year she did do a big pooh in the bath!)
This really doesn't involve that much effort, (particularly if you can get your DH to do the baking, as I do!) I just chopped up vegetables and opened the crisps! DCs made the chocolate crispy things and iced the biscuits.