A number of modern Polish and Catholic sources offer variations on this anecdote, as do some evangelicals in hilariously lurid form. Many people even remember it happening to them personally.
It strikes me as implausible for a number of ideological and practical reasons, and the oldest reference I can find cites a Mussolini-era Italian newspaper.
Does anyone know if there are solid contemporary references to support the story, or at least something like it? Was the Stalinization of Eastern Europe really conducted in such a heavy-handed, overtly idolatrous form?
For what it is worth, a similar episode occurs in the movie Europa Europa which is based on an autobiography by Solomon Perel, a German Jewish boy who was enrolled in Hitler Jugend but then saved by the Soviet army and enrolled as a Komsomol, which is where the candy episode happens. The kids are instructed to pray to Jesus for candy, and nothing happens. Then they are instructed to pray to Stalin for candy, and assistants then throws candy from openings in the ceiling.
I haven't read the autobiography the movie is based on though, and cannot speak to the veracity of the scene.