This quote comes at the beginning of Chapter 7, while the teachers are discussing Ender's progress at the Battle School. Since the children there are gifted, and since they are put through tests and hardships that most other children never experience, the children at Battle School are more adult than is typical:
"They're the most brilliant children in the world, each in his own way."
"But shouldn't they still act like children? They aren't normal. They act like -- history. Napoleon and Wellington. Caesar and Brutus."
(Card, Ender's Game, Google Books)
The children form factions and align themselves behind leaders because they have little adult supervision. Being forced to act in adult ways changes their mentality, and since the Battle School is military, they start to think in military ways. This shows how pragmatic the Battle School is in creating leaders for war; it is harsh, and some call it inhumane, but with the existance of the human race at stake, it works. These children lose their childish innocence quickly, and become capable of making decisions that affect others.
The actual quote you are referring to is, “They act like—history. Napoleon and Wellington. Caesar and Brutus.” The “someone” you are referring to is the unknown characters who speak at the beginning of each chapter, giving you a small hint of what is going to happen in the chapter (foreshadowing). To completely answer this question you have to know who Napoleon, Wellington, Caesar and Burtus are; they are famous historical military leaders. The question wants you to think about how these children are like the adults from history. There is one ironic part of the statement, the fact that these children are being compared to historical adults, which is not something that can be said about most children.