If your child wants to dress as a swashbuckling hero for a fancy dress party, be different with an "old-school" idea instead of dressing him as one of today's superheroes. As a bonus, you won't have to "steal from the rich" when you use basic materials to make this Robin Hood costume.
Buy two t-shirts, one deep green and another in white, gold or brown. Get shirts that are several sizes too big so they will look like tunics.
Cut evenly spaced, 2.5 cm (1 inch) square notches from around the bottom of the green shirt so the hem ends up looking like a chunky fringe. Layer the green shirt over the shirt that you didn't cut to create a two-toned effect.
Find a wide brown belt to cinch the shirts in at the waist to look like a tunic. Match the color to the pair of brown leather shoes or boots that he'll wear with the costume.
Pair the tunic with a pair of green tights. If your son is too self-conscious to wear tights, try thin green pyjama or jogging bottoms.
Create a hat with two pieces of green felt cut into elongated triangles. Use simple stitches of fabric glue to join the pieces together and embellish the hat with red and yellow feathers.
Get a toy bow and arrow set that resemble weapons that Robin Hood would carry. Stash the arrows in a "quiver" that you've created with felt. You can also turn a long, narrow tote bag or even a wine bottle caddy into a quiver in a pinch.