This actually sounds like conditioning camps for child-soldiers.  Where orphans, as well as kids who're kidnapped from schools and homes, are taken, conditioned and mistreated to brainwash them into becoming soldiers.  It's a very common thing to do in cults, too.  To condition the kids using harsh treatment and the reward / punishment, as well as deprivation, into full obedience.  This often includes taking away their names, their very identities, breaking them until they can shatter no further, then rebuilding them, brainwashed, into cold, ruthless, obedient, solders.  The "mean girls" were probably ones who wee already past the broken stage and now were into the brainwashing stage.  Though the group that broke in to take all the kids out of that place will actually have a harder time with the "mean girls" and other kids who have turned violent, than they will with younger, frightened, ones like Ciel.