2 paper grocery bags, pipe cleaners, construction paper
Get two large paper grocery bags for each child. Cut a large oval out of the bottom of one bag. Slide it into the other bag, open end first, so that the oval is on top. The oval will be the monster's mouth. Decorate the top of the bag with construction paper eyes, mouth, hair, whatever. Poke a small hole on the top of the monster, about 2" from the back edge, and another hole on the back of the monster, about 3" from the top. Run a pipe cleaner through the two holes and twist together to make a handle. Then take the monsters for a walk and "feed" them any trash you find. This monster also looks cute as a trash can in the child's room. To empty and reuse, untwist the pipe cleaner and pull the top bag out, empty and replace.