@thornekey - ‘pretty sure’ isn’t a good legal defense, especially when it’s bad advice. i know that you’re just trying to help, but be certain that you are 100% correct before posting something.
regardless of the game being free/educational/etc. you MUST get permission to use characters not created by you or somebody who grants a license to use them. something like Spiderman/Batman/etc. will DEFINITELY need some license so save yourself getting into BIG trouble by not doing it.
i’ve been making games for a very long time and have a lot of experience with licenses, etc.