Yes and no.

The first openly discussed case of a child poisoned by candy was an attempt at insurance fraud.

It happened in 1974 in Pasadena, Texas, where a father, Ronald Clark O`Bryan, took his children and a few other kids on a round of Trick-or-Treating in his area. Some of the candy collected was a number of pixi-stixs, small tubes filled with powdered sugar candy, which the father divided amongst his two own children and the three others he had with him. Afterwards it was determined that all five pieces of candy had been opened and poisend with a type of cyanide, then closed again. His son consumed one of them later the same evening, and, although the child alledgedly noticed a bitter taste, the child consumed enough to become sick with strong cramps and die just shortly after on his way to the hospital. Police was called, and Media also started to report very quickly on a case of a child poisoned by trick-or-treat candy causing many parents to hand their candy over to the police out of fear. As the word spread the parents of the other 3 kids were alarmed and handed in their candy, too, luckily no other child had consumed their candy yet, so nobody else died. At first, after police was called, the father claimed he couldn`t remember where they had gotten these particular pieces of candy, and who they might have gotten them from, but it soon turned out to be a lie. The Father had evidently prepared the powdered candy and given it to his son to kill him and claim the life insurance money, while all the other kids were supposed to create the image of an unknown killer poisening children while trick-or-treating.

O`Bryan hasn`t openly admitted to killing his son, but the trial later showed how he had not only insured both kids kids for about 20k each, but also had given his son the candy purposefully, and offered him something sweet to drink to cover up the bitter taste the kid complained about instead of taking the strangely tasting candy away. He was in dept too, and it was argued that he had planned to poison his children to cash in on the insurance and cover his depts. He was pronounced guilty in 75 and put to death in 1984. [1, 2, 3, 4]

Media, of course, run with the case and he was dubbed The Candy Man - either by his inmates or the media. And although there have been some cases over the years since then where people claimed to have been hurt by either poisened candy or candy prepared with glass or razor blades, cases that actually came from random strangers with bad intentions were few and far between. The fear is still present though.

A researcher named Joel Best, working for the University of Delaware, did some research about what he called Halloween sadism, or the phenomenon of a sadistic strangers causing damage to innocent children via halloween candy, but only found a few cases in which children did suffer by what seemed to be a case of trick-or-treating gone wrong and none really comit by strangers. Amongst the five cases the media atributed to such instances at first, the O`Bryan son amongst them, he found not much evidence that there really was ever a case of true halloween sadism done by random strangers but several cases of accidents, medical conditions, or ill will by close relatives. In most cases, it was the media spreading the approach about how someone random hat poisoned the kids before the real, often different reasons would become known. [5]

So, you see, Yes, there was an actual case in which a child died due to poisoned candy, and no, since it wasn`t a act by a random angry stranger to hurt children - the fear so many parents cite nowadays as a great fear when going trick-or-treating with their children - but usually either a unlucky accidents, conditions following natural causes or sickness, or someone within the family, as in the O`Bryan case, having bad intentions.