One of the things my kids liked when they were little, was "Halloween Week". That week, we hung paper bats all over the house, would do craft projects and I'd try and make something creepy or gross for dinner....
This is a great idea and it doesn't really take much prep at all. You could even get one of the pre-packaged "Taco Kits" that has most of the ingredients that you'll need.
Also be sure to pick up some flour tortillas, cheddar cheese slices, black olives, sour cream and salsa, you'll need it to decorate the tacos.
I'm sure you'll hear lots of crunches and giggles from your little monsters around the dinner table!