As in all totalitarian states, the authorities in Oceania realize the importance of catching them young: of indoctrinating young people into the fanatical left-wing ideology practiced by Ingsoc, the ruling party. The Party clearly believes that by establishing the Junior Spies organization, they will be nurturing the next generation of loyal cadres, thus ensuring the continuation of the regime.
To some extent, this process of indoctrination involves separating children from their parents, dissolving the natural ties between parents and children so that the children of Oceania belong to the state. The Party wants all children to believe that Big Brother is their mother and father all rolled into one.
Such ideological indoctrination can be seen in the activities of the Junior Spies, a Party organization whose child members are encouraged to keep tabs on adults—including their parents—to make sure that they don't do anything disloyal or treacherous.
Mr. Parsons's children, zealous members of the Junior Spies, turn in their own father to the authorities on the basis that he's committed thoughtcrimes. This demonstrates the extent to which children have been separated from their parents: they owe their primary loyalty to the Party and not to their own flesh and blood. Mr. Parsons's children have become so thoroughly indoctrinated by the prevailing ideology that they can't wait to see the state's political enemies publicly hanged.