Begin by inflating your balloon. You can make pumpkins of varying sizes by adding more or less air to the balloons.
Glue the driftwood pieces in triangle shapes and build them out around the entire balloon, taking care to glue the pieces to one another and not to the balloon so that the hot glue doesn't pop it. Fill in the driftwood pieces enough to form a solid sphere.
When the glue is cool and dry, pop the balloon. Lastly add a stem piece to the sphere to make it look like a pumpkin.
Notes
You could paint these orange or leave them natural coloured.Store your DIY wood pumpkins carefully and use them year after year.