Kirsti is the bratty little sister we all love to hate. But we like to think of her as the portrait of innocence in a far from innocent world. This girl doesn't even realize that foreign soldiers are a threatening force:
For Kirsti, the soldiers were simply part of the landscape, something that had always been there, on every corner, as unimportant as lampposts, throughout her remembered life. (1.40)
This innocence actually protects Kirsti from the terrors of war. When Annemarie thinks back to an encounter the two of them had with a soldier, she remembers, "Kirsti hadn't been frightened. Kirsti had been—well, nothing more than a silly little girl, angered because the soldier had touched her hair that afternoon. She had known nothing of danger, and the soldier had been amused by her" (15.3). Kirsti isn't scared because she doesn't know she should be.
But Kirsti ends up playing a big role in Annemarie's journey through the war. She charms the pants off of Nazi officers and keeps Annemarie and Ellen entertained. And in fact, when Annemarie encounters the soldiers on her scary delivery route, she uses Kirsti as her model of a "silly little girl" to stay out of trouble. Maybe this isn't the most flattering version of Kirsti—but why should it be? Kirsti's only five. She is a little girl. Why shouldn't she be silly?
By the end of the book, Kirsti has changed—she's matured. When the Danes celebrate the conclusion of the war, Kirsti isn't left out or put to bed, like she had been before:
Kirsti, waving a small flag, sang; her blue eyes were bright. Even Kirsti was growing up; no longer was she a lighthearted chatterbox of a child. Now she was taller, more serious, and very thin. She looked like the pictures of Lise at seven, in the old album. (17.6)
Kirsti may look like Lise, but she will grow up to have the future that her older sister didn't get to have. How's that for hopeful?