I think what you want, then, is simply Minecraft Pi, not MineOS.
MineOS is ideal for when you’re trying to have a server distribution host Minecraft instances, but Minecraft Pi (the educational project) is itself aiming for something very different (and fundamentally not compatible).
https://www.raspberrypi.org/learning/getting-started-with-minecraft-pi/requirements/
While MineOS operates on Raspberry Pi’s, it’s really a very niche audience who would want to make that thing happen. For your kids, You’ll want to have a RPi for each child, because each child will also want to have a screen and keyboard to work with it.
Now, I understand multiuser is a goal (perhaps $ limited?), but while it is probably very possible to have virtual desktops that different users can log into, the hardware behind an RPI is probably too weak to handle more than one simultaneous Minecraft: PI Edition instance along with the IDE.
TLDR: Minecraft: PI Edition is not something you could work together with MineOS–their aims are not compatible.