Ender's Game, like most science fiction, takes societal "givens" and twists them in strange and compelling ways. One of the main "givens" thus experimented with is that of childhood, or the notion of childhood as discrete from, and inferior to, adulthood.
In the book, hyper-intelligent children are separated from their families and sent to Battle School, where they study military strategy, and train to become great generals. These children are infinitely (and necessarily) more intelligent than most adults, much less children; also, they comport themselves in ways we would not except of young children. Ender is about 11 when he passes his "Final Exam," and unwittingly destroys the Formics.
How many eleven-year-olds do you know? How many of them would be capable of not only leaving their families and living in a strict, violent military academy, but of leading large platoons and waging intergalactic warfare? How many would be able to survive the emotional and psychological stress that comes with being expected to save the world? Indeed, the children's of Ender's Game are advanced in all aspects.
As we can see, childhood does not exist for these students; their behavior, as well as their genius, sets them apart from "normal" children. Hence, they challenge our typical notions of childhood, innocence, and development. However, it is by studying the adults of Ender's Game that we truly appreciate its imaginative scope, and its troubling of concepts. These "grown-ups" are incompetent, negligent, and downright sadistic; they do not care for the well-being of the children at Battle School. Graff even admits that his job is to produce the next Alexander the Great, not to nurture children. He goes on to imply that Ender's health is of secondary importance. Graff and his colleagues are supposedly responsible adults, yet they ship innocent children to battle school, and expose them to incredible pressure, pain, and trauma. They also lie to and manipulate the children on a regular basis; Ender is initially unaware that his "Final Exam" is actually a war. When he does find out, he seems to have a complete nervous breakdown. As always, Graff's lies have terrible consequences.
Graff and his colleagues are trying to save the world. They feel that if they do not succeed in producing that next Alexander, they will be unable to stave off the Formic Invasion. But does this justify their atrocious treatment of the children at Battle School? We should also note that, despite their stated goal, they are grossly negligent in terms of basic school management. For example, Ender is acutely aware that Bonzo Madrid is mentally unstable, and that the school administrators will do absolutely nothing to prevent him from hurting others. This negligence is what ultimately leads to Bonzo's death, and yet another traumatizing experience for Ender. One would think that, in order to create the best and brightest generals, the administration would be more vigilant, and ensure the children's safety.
It is perhaps their utter lack of empathy which is most troubling among the adults. On the other hand, empathy is surprisingly plentiful among the children. Whereas Graff and his colleagues do not really care if any particular child lives or dies, the children often go out of their way to comfort, nurture, and support each other. After the "Final Exam," Petra and the rest of Ender's platoon dote over him as he recovers; Ender went out of his way to counsel and befriend Bean, just as Petra had done for him earlier; Dink Meeker is noted for his unusually kind manner. The children, in contrast to the adults, band together, and protect each other from the rapacious environment of Battle School.
Thus, in Ender's Game, hyper-intelligent children are more empathetic, and often more moral, than their adult counterparts. Whereas adults are cruel, negligent, and myopic, the children care for each other, and are sometimes able to perceive the injustice of their situation (especially Dink).
Ultimately, the novel asks us to reconsider what it means to be a "grown-up." The children of Ender's Game are not only more "grown up" than their teachers in terms of intelligence and competence, but also in terms of empathy, morality, and community. It could be argued that, in a world of invading aliens and vicious adults, the children are the only human element in all of Ender's Game.