I've modified a document from Super Fun Printables. The original document was free, but came with the jack-o-lantern face pre-printed on it, which seemed like a wasted opportunity to me, especially since I knew my elementary schoolers would have fun drawing a jack-o-lantern face themselves. So I just removed the face.
I recommend printing on cardstock or thick craft paper. It's formatted to be printed out on A4, but it can also be scaled to work on B4.
Print out however many copies you need; hand out to the students; let them draw the faces; cut out the two pieces (remind students not to cut off the half circles: these will be used to connect the sides to the pumpkins face); and finally use glue or tape to attach the sides and the handle.
Afterwards, you play trick or treat with stickers or whatever treats or prizes your school will allow.
This is so cute!