Controlling Purpose

I guess for my essay my controlling purpose would have to be about if children get Stockholm syndrome more than adults. I spend a lot of time analyzing why its possible that children get it more than adults. I'm also wondering if I should talk about adults more in my paper or if that would be going beyond my controlling purpose. I'm starting to wonder if my controlling purpose is too specific for the amount of sources that I have out there. I'm finding difficult to get beyond five pages without starting to repeat myself.