I have been going through my clothes and getting stuff ready for goodwill, so I already had some shirts on hand. They are all t-shirt material. I cut them up the middle front if there was no design, but if I wanted to utilize a design, I just flipped the shirt and cut up the middle on the back. It's very versatile. I made sure to stop cutting before I got to the collar. Then I cut in a diagonal line from the bottom up to the underarm. Then I repeated this on the other side. Finally, I tied the ends.
I plan on putting letters on the capes for each kid. If you use a long sleeve shirt, you can easily add leg guards or arm guards for the costume. Also if the shirt is a button up, you can utilize that. I also used some short sleeve stretch t-shirt sleeves for masks. I just cut out eye holes. No need to sew, but if you want it'll look more finished. This is easy to make, personalize, customize, and embellish. Best thing, it costs nothing but a little time.