The Mother of Inventions
In her case, it's easy to understand what's going on. Her grandmother died recently, and this is one way that she's been processing that, in a perfectly age-appropriate way. The games she plays with her older sister have also reflected this process; many of their characters seem to have been recently bereaved.
But what motivated the people who invented Sgt Dan Kennings, used him for two years of anti-war propaganda, and eventually killed him off?