Interchangeable capes... wow, I guess not only your nephews would like them. It would be too cute to have this possibility on a project bag. I have never attached Velcro neither have I tried to make such a logo myself, both seem like fiddly work. But your logos turned out beautiful.
I am not very knowledgeable in the superhero realm, but I just now watched a serial about anti-superheroes which was fairly brutal but also ironic and with a lot of dark humour:
https://www.imdb.com/title/tt1190634/
Do you know this/like this?