Weapons
This movie reminded me of a conversation my classmate once had w/ his mom back in elementary school where we were both curious about why kids in older books could spend all day outside exploring the neighborhood without parents caring at all. All she could say is that it was safer back then, which is true in part, but I do think mass paranoia - distrust of people outside of their own communities has festered into a sword pointed at all outside of the household - has contributed to it. Back then, parents could rest easy that their neighbors would have their best interests in heart, abiding by an unspoken honor system that has long since festered. The parents in this movie had security systems, ring cameras to monitor their front yards, and a watchful eye on the school at all time; but despite all of these precautions, preparing themselves w/ the notion that not even the teachers were trustworthy characters (see: the principial constantly telling Justine to maintain a distance w/ students at all times due to parents' complaints), they were still caught unaware. Tragedy still struck them, despite everything they've done 'right' to prevent otherwise.
This movie works so well because it feels like a fairytale in that aspect - reminiscent of both Pied Piper and changelings - where the kids are lost to a mysterious third party, and once found, are not the kids they once knew. It's a cautionary tale where their worst fears are realized: even in their own neighborhood, their kids will always be in proximity to some threat - foreign or neighborly, eventually to be used against them as a weapon of somebody else's making.