I've just given 2 parties - for a 7 and a 4 yr old - so hopefully have a few, hard-earned pearls of wisdom to impart!
I found the following website invaluable when I was panicking beforehand. It's geared at parties at home, but there are useful tips, and it's very amusing to read!
www.kidspartysurvivalguide.com/tccpsg.html
Pass the parcel tip: I've spent years wrapping up the exact n/o layers for the exact n/o kids, and one really useful tip from this survival guide is, don't do that! It just takes too long, and the kids get bored waiting for the parcel to go round and round. Make each kid do a forfeit perhaps instead of getting a sweetie at each layer, that could be fun.
Kids don't mind if they don't win a prize. Keep the prizes small and simple in any case, just one small sweet is sufficient - the excitement is in the party itself.
Have you thought of fancy dress? I always think this is a brilliant ice-breaker, and there's an immediate party atmosphere.
Discipline. Sit them all down early on and explain what's happening, the programme etc. Be firm from the beginning. Anyone who's playing up, tell them that they'll have to go home early - they soon get the message. Don't tolerate bad behaviour.
Have sthg that makes a noise, that will tell the kids when it's time to stop and listen.
Dress up as a clown or sthg yourself, or maybe wear a funny hat, then the kids know which adult is the focal person to listen to.
Party games. yes, it's a brilliant age for games, but don't attempt too many. Have a few up your sleeve just in case, but you can fill up a lot of time just dancing in eg musical statues, bumps etc. Just have freetime dancing do, with the conga (spelling?) etc.
Food: I've spent years doing lots of little bits and pieces for the kids to eat. This year I did a couple of huge pizzas and chicken nuggets. I cut the pizzas into SMALL squares, and it all went down a treat. Small meant hardly any waste - there was plenty for seconds, but not much left on the plate. Same with the cake - Small slices. Keep some for parents at the end too. You could always cook the food beforehand and take it to the hall, it needn't be piping hot to serve.
Party bags. I named all mine so that I could tailor boys/girls or younger/older children, but if your party is all the same age group, keep things simple and keep the bags all the same. Have a couple of extra just in case - maybe a sibling will stay on, or someone else turn up at the last minute! And maybe have extra sweets or sthg handy to give to siblings who arrive too at the end of the party. It's so easy to do, but it creates a nice atmosphere, and the parents appreciate it.
Phew! Am getting carried away with my rosy-tinted memories. Better do some work instead! The main thing is, keep things as simple as you can.
Good luck! Enjoy! Don't forget your camera!