My sons have requested to be a knight and a prince-knight for Hallowe'en this year. You can't have a knight without a sword and a shield. This one is pretty straightforward to make, especially if you've already made the felt sword with the replaceable insert.
(1) Design the basic size and shape of your shield, keeping in mind that the widest point of the shield needs to be at the top (i.e. where the opening to the cardboard insert will be). Cut a template out of cardboard and keep this one handy, you'll need it to trace the shield and to cut additional inserts once the first one starts to get bent.
(1a) Optional: Tell your son that the cutout box is a robot costume to keep him out of your hair while you're working.
(2) For each shield, cut one shield out of black felt, one shield out of some kind of backing material (I used black broadcloth. You'd probably not want to use felt for the backing because it would pill a lot with repeated use of the armband).
(3) Embellish your shields as you see fit. I've sewn on some felt embellishments, but you could also glue on whatever your little crafting heart desires.
(4) Attach an armband to the backing. I used some satin blanket binding tape to make single armbands, simply because I had some leftover from a related project. However, I think two, parallel armbands made from wide, black elastic would be great. If you're using elastic then you wouldn't have to attach the armbands as loosely as I did in the photo, because they could stretch to fit the wearer.
(5) Overcast or serge or otherwise finish the top edge of the backing if you've used a fabric that will fray.
(6) Sew the front and back pieces wrong-sides together (right-sides facing out), leaving the top open for the cardboard insert. At this point you could also attach a small snap or piece of velcro if you want to be able to seal the top. I left the top of the shields open because it was easy :)
(7) Insert some cardboard and defend your king!
p.s. When cutting out the insert, trace your template and cut about a 1/4-inch inside the template line.
Notice the Knight's tunic? That's the pièce de résistance and it's coming up next!