I saw this super cute idea on Pinterest and it was done by Parents.com. They are really simple and easy to make for a kids Halloween party. All you need is some white electrical tape, googly eyes, and juice boxes! You can find more details here from Parents.com.
I used the small sized juice boxes. You just remove the straw and wrap the box in tape. Punch a hole in the tape for the straw. Then stick on the googly eyes and put one or two extra pieces of tape over the eyes to make some different faces!