The boy
Pavlik Morozov — never referred by the proper first name, Pavel, or any other variant, akin to Johnny Depp (thanks to the rubber-stamping nature of the media, in both cases) — gained fame as a 13-year old boy from the village of Gerasimovka in the western Siberia. In the end of 1931 he denounced his father Trofim, engaged in some forbidden activity, to Soviet authorities. Records vary on what "crime" the man had committed; the most credible version says that he, being the chairman of the local kolkhoz, provided papers to exiled peasants (kulaks) that allowed them to return home. According to some accounts, Trofim had also left Pavlik's mother for a mistress; this may shed some light on the negative feelings his son had toward him. The father was convicted and sent to a prison camp. Some reports say that Pavlik continued to be an active informer after that, pointing to his other relatives. On September 3, 1932, Pavlik Morozov and his younger brother were killed in a forest near the village. The investigation quickly rounded up Pavlik's relatives: his cousin, 19 years old, his grandfather, 81, his grandmother, 79, and his uncle, 70. They were found guilty despite total lack of evidence (if Stalin's maxims about ever-vicious enemies of the Revolution do not count) and shot shortly thereafter.
The myth
Pavlik was quickly canonized by the Soviet domestic propaganda. There was a persistent strife with "enemies of the people" in 1920s-1940s; this required heroes and victims to feed the flames of the people's rage. Pavlik's "feat," as it was taught in schools, was adapted to look more righteous and less of a family quarrel: it was told that he informed on malicious kulaks who concealed hoards of bread and intimidated the poorer folk, his father and granddad being among them; then he was slain by the villains remaining at large. He was set as a model of truthfulness and adherence to the principles of the Stalinist state, to the point of neglecting family ties and personal safety. He was posthumously enrolled in Young Pioneers, the Soviet equivalent of Boy Scouts; his membership number was set to 001.
The debunking
After decades of mind-numbing praise, it's no wonder that the icon of Pavlik Morozov has reverted to a loathsome antihero as soon as the Soviet myth ceased to support itself. Today, 70 years after Pavlik's death, his deed is looked upon as horribly wrong in his mother country, despite his being, after all, a murdered kid. Nobody would teach children to be as "pure-hearted" as Pavlik and eagerly give away their parents as soon as they run afoul of the General Party Line.
Sources:
http://www.ntvru.com/dosjex.html?lid=17403
http://www.cyberussr.com/rus/morozov.html