Pull the Worms Out!
Before the party, prepare two large sheet cakes. Before you frost the cakes, place as many gummy worms as you can inside them. Once you decorate the cakes with chocolate frosting and cookies designed to look like headstones, set them at either end of a long table. Divide the players into two teams and have each team stand next to a cake. When you say "Go," all the players have to find the gummy worms inside the cakes. The team to find all its worms first wins the game.
Ghost Detective
Select one player, perhaps the birthday girl, to start the game as the ghost detective. Once she leaves the room, pick two other girls to leave the room. Select one player to play the ghost, and place a sheet over her head. Bring the ghost detective back in the room. She studies all the players in the room and has to guess which person is hiding under the sheet. If she guesses incorrectly, tell her to leave the room so you can pick another ghost and shuffle other players in and out of the room. Once she guesses correctly, another player gets to play the ghost detective. Play for as long as you like.
Halloween Dress-Up Relay
Gather up several Halloween costumes, picking costumes the girls can easily put on over their clothes. Divide the players into two equally numbered teams and place a pile of costumes, one for every girl in the group, in front of each team. When you say "Go," the players all put on a costume in the pile. As soon as they put the costume on, they take it off and hand it to the player next to them. The first team whose players have tried on all of the costumes wins.
Tricks and Treats
This game easily incorporates giving out party favors with a bit of trickery. Prepare by writing out 10 words on a white board that have to do with Halloween or birthdays. For example, use words like "witch," "cake" and "ghost." As soon as your guests arrive, hand them a bag of goodies and tell them they cannot say the words on the board or they lose a treat from their bags. Anyone who catches a player using a forbidden word gets to keep the treat the other person loses. The person with the most treats at the end wins.