To do this project, I googled and googled until I found a pattern that would work for me. That means, not too difficult, but cute and durable. I found the best tutorial at http://www.howdoesshe.com/super-hero-cape/. She does a great job explaining the pattern, and the collar uses velcro to fasten instead of tieing a string (which I think is a bit safer).
Once the cape was sewn, I needed to find an emblem for the back. I made these out of felt. I googled the batman emblem, and just "eye-balled" it when cutting and designing Batman's logo. For Emma's, I free-handed the lightning bolt and her first initial. I sewed the initial on top of the bolt before sewing it onto the cape. I used my sewing machine to sew onto the cape by outlining the emblem.
Lastly, it was time for the masks and crowns. I made these out of matching felt as well (to match the emblem). I found great templates for these via www.firstpalette.com. I just printed the templates that they had on their site and traced them onto my felt (http://www.firstpalette.com/tool_box/printables/superhero.html). When creating the masks, I doubled them up with two pieces of felt to make them more durable. I used elastic to wrap around the head, and affixed the elastic my sewing it. I sewed around the border of the mask/crown, and then sewed around the eye-holes. Then, I just trimmed it up to make it look nice, and I was ready to make my kids super-heros.
They loved them more than I thought they would! I can't wait to give them as gifts. I would love to make more of these -- so much fun -- I just have to find some future superheros to make them for.