No child has ever been killed by poisoned candy. Ever.
Take "stranger danger," the classic Halloween horror. Even when I was a kid, back in the "Bewitched" and "Brady Bunch" costume era, parents were already worried about neighbors poisoning candy. Sure, the folks down the street might smile and wave the rest of the year, but apparently they were just biding their time before stuffing us silly with strychnine-laced Smarties.
That was a wacky idea, but we bought it. We still buy it, even though Joel Best, a sociologist at the University of Delaware, has researched the topic and spends every October telling the press that there has never been a single case of any child being killed by a stranger's Halloween candy. (Oh, yes, he concedes, there was once a Texas boy poisoned by a Pixie Stix. But his dad did it for the insurance money. He was executed.)