The pattern is here: [link]
I made my pumpkin out of fleece, but you can also use other stretchy fabrics like doeskin suede, stretch velveteen, minky or even short pile fur fabric. It won't look quite the same in a non-stretchy material like felt, quilting cotton or corduroy, but they can still be used.
It's sized to print out on 8.5 x 11 paper, but you can shrink it for a palm-sized pumpkin or enlarge it. The size of your pumpkin will determine how much fabric and stuffing you'll need.
If you're making a very large version - pillow sized, for example - you might prefer to make the stem from a sewn cylinder, and to make the leaf stuffed. In that case, cut out two leaves, one with the pattern flipped so you have mirror images, with a 1/4 inch seam allowance, and sew together right sides facing, leaving a small opening at the stem end to turn though, then turn, stuff and sew to the pumpkin.
You can easily make it into a Jack O'Lantern with glued felt, painted, appliqued or embroidered features.
If you're making several pumpkins, they look nice in slightly different sizes, with different shapes and numbers of leaves.
If you're throwing a Halloween party for the little ones, these make great beanbags for a pumpkin toss game - you can use something like a plastic witch's cauldron or a posterboard monster with a cut-out mouth as the target. Weight them with plastic beans, or if those aren't available, use dried beans or rice (although these will deteriorate over time or if they get wet).