The annotated code of my state would classify this as misdemeanor false imprisonment, as there was no evidence that any specific individual should be restrained from leaving the facility, and definitely no indication 100 (or however many were present) were complicit - in fact, D&B wasn't even sure there was a problem when they were curtailing movements . . .

That said, I would have used the Blackberry to look up the non-emergency number for the police and let them know of both situations (child missing with slow response by staff and restraining customers).

On the Twix example above - questioning an individual would only be allowed if there was a reason to suspect shoplifting; eating lunch at a restaurant doesn't make one a "suspect" who can be detained in a missing child instance where ideally no crime has been committed. One cannot question all current customers because someone previously stole a Twix bar from the store . . .