So, I made this knight costume as a Christmas gift for my step-son. He's 7, and loves playing dress-up. I'm really, really proud of it. All told this project took me a good 4 days of work!
I designed it myself, drew the wyvern (inspired by images I googled), and did most of the details with a blanket stitch by hand. The "shirt" is reversible, so he can either be a "George who slew the dragon" style knight or a Crusader (not that I think the crusades were a good thing). There are snaps on one shoulder so I wouldn't have to worry about his head not fitting through the hole, and I installed elastics around the torso for an easy fit.
The shield has two pieces of cardboard hidden within to make it sturdier.