These distinctive cover-ups are a cinch to craft out of black foam and sewing elastic. Before the party, make a patch for each "pirate" on the guest list and they'll be ready to custom fit when everyone arrives.
Download Pirate's Eyepatch TemplatePrint out the template and use it as a pattern for cutting an eyepatch out of black craft foam for each child.

Working with one patch at a time, snip a 1 1/4-inch slit in the bottom, as shown. Then glue the cut edges back together so that they overlap a bit, causing the patch to cup slightly.
Next, use the tips of the scissors to make a small hole in each of the upper corners of the patch.

Cut a piece of thin sewing elastic to a length that is just a little longer than necessary to fit around a child's head. Thread the ends through the holes in the foam from the front of the patch, as shown. Then knot the elastic ends and gently pull them into place so the knots rest against the foam on the inside of the patch.
This craft is a part of these parties: