Judging from the final comment in this comic, I thought that this was actually ground zero. That the group has escaped to a former "Plutonian fortress of solitude" that Qbit acquired, but had never visited.
This, then, implies that these were presumably test subjects. Judging from the number of child skeletons with two adult skeletons, it was some sort of nursery. I'm not sure why the Plutonian has a nursery. Were these his kids?
It seemed obvious to me that the Plutonian has a connection to the "sonic virus" in some way. Whether he created it, discovered it, always had it, or whatever isn't completely clear.