Cut out a large oval in green construction paper. Draw and cut out some hands/legs for the monster in green. Use some white paper and cut out an oval eye, and some horns while you're at it. Give your kiddo the glue and let them slap that down on some background purple paper.
While they're doing that, tear up some tissue paper, I used green and blue, into smallish pieces, maybe 2x2inches?, show your kiddo how to crumple them up, and then glue down the crumpled up paper to be the monster's fur. Go for good coverage on the fur, it'll look cute AND it will keep them very busy, double bonus!
When they are done with the fur have them glue on the horns. And now the eye, Zach is enamored with googly eyes right now, in case you couldn't tell, so he used a bunch of those on the white oval to make the monster eye.
Let the glue dry. Hang the beautiful and festive creation in a proper frame to adorn your home with DIY Halloween decorations.