Bake gingerbread boys and girls (at least four cookies per child, plus a few extras in case any break), and mix up three or four different colored icings, which you can refrigerate in lidded containers. This party's all about creativity, so make sure you've got lots of decorations to choose from, like gumdrops, mini marshmallows, and chocolate candies. And don't forget to stock up on paper towels for quick cleanups.
Control the mess (and the meltdowns) by setting up a workstation for each child: a place mat, paper plate, and cups filled with decorations. Put paintbrushes and open containers of icing down the middle of the table so everyone can share.