Use any round object and draw a circle around it. This one I used for the smallest pumpkin and it measured 10 inches in diameter. The middle one was 18 inches, and the largest, 24 inches.
Paint the fabric with craft paint diluted with some water. Using a sponge brush paint one side of the fabric. Allow to dry.
Cut out each circle, and sew basting or gathering stitches. Do this by threading a long piece of thread through your needle to the half waypoint. Gather the ends of the thread and tie a knot. Then sew up through the fabric about 1/4 of an inch from the edge. Sew nice wide stitches until you reach the other end.
Pull-on the thread to gather the fabric into shape. You can pull it all the way closed or leave it a little open like the one shown above to get it a flatter shape, it will be covered if you are going to stack them. Make a knot by sewing close to the end and threading the needle through the loop.
Stuff the pumpkin with batting or polyfill.
Make a stem by cutting a long rectangle and painting it green. Then roll it up and glue the edge. Glue the stem into the pumpkin.
Add a vine by using a piece of green wire or a pipe cleaner, and wrap it around a pencil. Glue into the pumpkin.
Stack your pumpkins on top of each other. You could secure them with glue or sew them together if you want to.
Add a little hay, moss, or other fall material to give it an extra rustic look.