Somebody squirted water inside a brand-new Sheriff's patrol car last year and destroyed thousands of dollars' worth of electrical systems. As you correctly note, Kimberly, it wasn't just kids who ran amok with Silly String. It was adults, too. Now, any adult who doesn't know better can get his butt hauled off to the local lockup. In a word, they aren't ours.
Nobody seems to know where they come from.
The parade committee can't kick them out or tell them what to sell. The city has no means of regulating them except to check for a valid State of California business license and, if they sell food, a county health permit. So the upshot is, even if people buy it, they can't use it. I hope this satisfies your request. With a little help from the Sheriffs, we'll have another great parade this year.