Thanks for the cape comments. If anyone else would like to make a cape for the little superhero in their life there is a PDF with a pattern piece for the collar, a star template and some (basic) instructions here. It's a very simple project, and a nice alternative to the commercial nylon costumes.
Let me know if anything in the pattern isn't clear or you notice any errors. And if you do make a cape I'd love to hear how it went.