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.
Most of the kids this days used to read comic books. That's why it's a good initiation to let your kids reading a comic book for Bitcoin. But we have to be aware not to force them because it only mean that it's not the right time. Maybe some time they are ready just wait patiently. "There is a saying that we just don't always drink milk, we also try to eat some hard food to live". My point here is that, don't surrender on helping your kids getting knowledge on Bitcoin, time will come that they will be ready for it, just trust the process.