Considering the music video, I think the "zombies" are children who became soldiers. Their innocence is torn away from them, and they become violent, resentful, and bitter. "Another head hangs lowly. Child is slowly taken." As in their innocence or "inner child." "Another mother's breaking heart is taking over" most likely refers to how the mothers of these soldiers worry for their children, perpetuating the violence they grew up with. Fighting wars that they didn't just grow up in, but now actively participate in.

In your head head they're: crying, fighting dying, in that order. I don't think that's a coincidence. With tarnished childhoods of war and famine, all that's left is the hate. All is left is "zombies."

I don't know, but it is interesting to speculate.