Board Thread:General Discussion/@comment-26849575-20160315015552/@comment-27701762-20160315023233

It at least seems like the previous kids were not incredibly violent, since Toriel appears to take care of all, if not most, of them, and if they were violent then Toriel should be dead.

While human souls have innate determination, the standard interpretation is that the red soul has an incredible amount of determination. It's not entirely clear what capabilities they have with respect to saving and resetting, given that A) Toriel has a line about always feeling like she knows the humans without meeting them, and B) Flowey comments that he had the power to SAVE until Frisk falls down. Even if they have some ability to reset, it would have to not be as powerful as Frisk's/Chara's, and as such they would not be able to save themselves if they died. And since pretty much every player dies at some point, positing that one of the previous children must have survived and become incredibly powerful would not be possible given the rules of the world, even one taking a "Genocide" path.