In 1984, what makes the children in his society so frightening to winston?

A book was written by George Orwell entitled 1984. 

In the story, he has a character named Winston who got afraid of how society changed the thinking of children in the story. The behaviors and conversations of the children he had talked to were not like ordinary children. They behave differently and have vicious thoughts running through their minds.
 
Children were used by their countries as spies during the war. Winston was afraid that these children would soon turn into soldiers.