Using royal icing, confectioners sugar and water or even store bought vanilla frosting, if the budget allows. Add candies, pieces of dried fruit, chocolate chips, nuts, raisins, etc. for features and details. Make enough to eat for refreshments and still have enough for each child to take one or two home to show off. I include some Halloween ideas in an accompanying article on the Dollar Stretcher site. Send these home, too.
Parties go much better when the kids get out, especially if the party is after school.
Play some playground games. Take advantage of what your community offers. Turn the spider web into a game by assigning each child a color to untangle and wind up into a ball for recycling. Webs can be made inside or out. They can mix punch, fill cups with pretzels, decorate the cake, scoop ice cream, etc.