Hey, at least they are following the rules. Security threat, possible concealed gun, then when the passenger is flagged, what looks like a hand-off?
I'd be more outraged if their security protocol could be breached by the social engineering of a smiling four year old. I'll save my outrage for the entire institution of the TSA existing; not on them actually doing their jobs.
Uhm, having DONE such security work before, I completely agree with zxcvbob. I suppose the difference is, there was a possibility of me actually dealing with hostiles as opposed to the TSA's knowledge that they are a dozen times more likely to get hit by lightning, several times in a row, than come in contact with a terrorist.
I'm not saying they're wrong to re-do the search. I'm saying they're completely unprofessional morons. I HAVE done this before. It's bloody easy. You have whoever is best with kids give the kid a spare teddy bear or similar stuffed animal, plus a cutesy story to keep them distracted, while the other guy or gal does the security sweep. Then explain to the parents or whatnot why it's a bad idea. Because bad people can use kids as cover, etc etc. Kid freaking out because you want to play jack boot thug is not a good thing. Gets crowds upset, gets folks hysterical, harder to control the situation, and makes more distractions that can cause you to overlook a real security threat.
If you're doing security work, you want to the bulk of the people to perhaps not like you but not actively hate you. Makes the folks more likely to give you heads up if nothing else. You're not nice (or polite and firm) because it's the morally right thing to do, it's to tactically handle the situation in the best possible manner.