That's a wonderful idea to introduce children to Bitcoin in a fun and engaging way! There aren't many comic books specifically focused on Bitcoin yet, but you can still find educational resources that explain the concept of cryptocurrencies and blockchain technology.
There are plenty of them but it will consume a bit of your time in searching one. This is really a good idea for giving the kids idea of what bitcoin is.
I did saw another thread about suggesting not to force kids into knowing bitcoin and that's also a good point.
Well it differs from the point of view of someone who like to share knowledge in bitcoin and those that are concerned for the welfare of kids so that they can enjoy their youth.