I think this one takes a little bit of work, but it could be really cool if you have a good imagination.
I seem to remember this activity where you get buckets and you fill them with different things…like in one you put spaghetti and sauce and you call it “innards” and then in another you put grapes with vegetable oil and you call them “eyeballs.” You can think up a lot of different things if you use your imagination. You could even fill a bucket with plastic bugs or gummy worms, or whatever you want. Then, you can blindfold the kids and write a little story (not too scary) that uses all of the things you put into the buckets. So maybe your story is like a Frankenstein story and you’re telling the kids about all the body parts that you need to make the monster. And when you say, “First, he needed some eyeballs!” And then all the kids have to reach into that bucket and feel them.
It’s kind of a fun way to tell a Halloween story and get kids involved. Plus, something tells me that 4th graders like to get their hands dirty. This might be a good activity for outside.