I'm going to expand on your theory because it makes total sense to me.
The children on the bench are members being indoctrinated hence the red shoes, red lips and white clothes.
I also believe they are the killers. Notice the hands, it's as if they just got done strangling someone.
The look of shock, like they just killed someone and now lost a part of their sole. The children below looking up at them scared. If the artist wasn't there to capture in real life, they painted from a picture.
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