A.M.
My college roommate and I created a Halloween scene for our dorm that might work for your little one's party: we turned a hallway into a scary forest. A roll of brown butcher paper, a box of cheap black trash bags, some fishing line, and fake cobwebs was all it took. Line strips of the butcher paper vertically to make "trees" (if you have a column somewhere you can use - even better!), twist butcher paper tightly to make branches and suspend them from the ceiling w/ fishing line (it's lightweight, so tape should work). Use the trashbags to cover the wall space between the trees, and hang the cobweb from your trees and the walls. Voila! A scary and inexpensive forest (better if you turn off the light and have an electric jack-o-lantern or very dim flashlight for the kids! Our dorm was open for kids to trick-or-treat, and it was a great hit w/ the kids.
Have fun with your party!