I know it's dark, but I'd be more concerned about suicide to 'join their child' especially if that was their only child.

My guess is some might have gone full faith in desperation to maintain a link to their lost child which is stopping physical acts of retribution in the hopes of spiritual retribution for the cowards that allowed their child's death and they also don't want to risk doing any acts that would deprive them a reunion with their child.

Again, I know it's dark but that's probably the truth..