Have you considered giving origami models as Halloween treats to celebrate both events?
Here are two simple but very nice models that you can fold for that purpose.
The models in the picture were folded with 12" (300mm) squares of scrapbook paper, but 6" (150 mm) regular origami paper will also work.
The instructions for both of them can be found in the book, Zoogami; An Origami Menagerie at Your Fingertips, by Gay Merrill Gross.
Happy World Origami Days and Happy Halloween!