There was something about this announcement posted at the Redwood City CalTrans station that pushed me to the snarky reaction in the title.
If the kids are under five, even six or seven, give them a pass with perhaps a smiling, gentle encouragement.
Older than that, it's harder to distinguish between a real disability and a squirrelly diagnosis designed to excuse bad parenting.
Calling kids out with deadpan sarcasm tends to get the message across. If they really have a legit problem, they probably won't get it anyway. If they're just being jerks, they probably won't get it until they're half-way to the next house. Something like:
"Great costume. You're really into it. You're supposed to be a kid with politeness deficit disorder, right?"