Explosive residue is sticky. If the kid was traveling with or was handling explosives, it would have been everywhere. Testing the bag and traveling companion would have resulted in even more alarms and more scrutiny.

Walking on fertilizer or working in a gunpowder-heavy industry might get you a false alarm for nitrates, and using certain colognes or hand lotions might get you another for nitroglycerin. Should the solution be eliminating all those tests altogether? Just because someone with ashy elbows wants to pre-lube before security instead of after?

Kind of ironic to complain about them "ignoring the threat", (a 9 y/o kid), as that's a direct result of other complaints. Everyone was up in arms about TSA screening grannies and children. Now they have alternatives, and people are still complaining.

It really doesn't matter what TSA does, so long as the rules only apply to everyone else.