One game we did last Halloween was you had a bowl of water, and you put a whistle in it and had to get it out with you teeth like you would in apple bobbing. The, you have a bowl of flour with marshmallows in it and while they're still wet from getting the whistle, you make them get the marshmallows out with their teeth. Trust me, it sticks to your face and in your hair and everywhere, it all got stuck to the roof of my mouth as well, it was horrible.

Another very simple one that everyone always loves at Halloween parties I've been to is hide and seek in the dark. We used to call it "Murder in the Dark" and we assigned a "murderer" and even had a fake Halloween axe for a "weapon". The "murderer" has to find their victims and put them all in one room and keep looking till they found everyone. If the kids at the party are anything like at the parties I've been too, they won't stay put in the room their put in and will "escape" which means the game can go on for ages and everyone will be screaming and laughing in no time.

If you have enough space outside, we also used to play a game when it got dark where you got a cola bottle (or any object really, we just used a bottle) and put it in on the ground. The adult (or several, if theres enough of you) carry torches and walk in a big circle around it. The players then have to get the bottle without you shining the torch at them. Play a few games of this, and if you can , after a few rounds get water pistols and suprise and soak everyone through when they come and try and get the bottle!
One other game we played was called "Trick or Treat". You make cards that say trick or treat on them, blindfold the person and make them pick a card. If they get treat, you can give them something nice to eat, if they get trick, something horrible. The person then has to guess what the food is - If they get it right, next time they get a treat, if they get it wrong they get a trick.
I don't know whether of these will be any use to you, they're just games I've played at Halloween parties over the years.