We've done several kids' Halloween parties. The two favorite games we remember are:
Donut Delight - Get a bunch of donuts equal to the # of kids at the party - cheap 12 for $1 ones are fine, although cider or fall seasonal ones can be fun. Tie an appx. 2-foot piece of string/yarn on each donut before the party. Then tie each donut to a clothesline or a line tightly stretched between two trees or items in your yard. Vary the heights/lengths. Each kid puts their hands behind their back, stands under a hanging donut and on the count of "3" or whatever, tries to be the first to eat his/her whole donut bite by bite without it falling and without touching it with anything other than their mouths. If it falls to the ground, the kid under that donut is out. Fun - with lots of giggles!
Wrap Your Mummy - Pair the kids off and give each pair one roll of toilet paper. Scott's is great, since it is not expensive and each roll is SO long! Each pair decides who is their wrapper and who is their mummy. When you yell "go" or whatever, all the wrappers race to wind their roll of toilet paper around the legs, arms, bodies, of the mummies. First team to use up their entire roll wins. Hilarious!
Good luck and have fun with your party!