Last night I was watching ABC's Nightline and they interviewed Tilda Swinton. At the end they talked about this new dark drama she was in called "We need to talk about Kevin". It's based on a 2003 book of the same name.
The movie's about her raising her first kid kevin and her struggles with him. Leading up to him pulling off a high school massacre as well as killing his younger sister and his dad. The film highlight's her parenting through kevin's childhood up to Kevin's rampage. Kevin seemed to have developmental problems and was highly resistant to toilet training. In the book his mom explains it as him waging a war with her and that him using diapers when he's surely capable of using the toilet is depleting her morale. The movie didn't nearly explain these situations as well, however in one scene she throws him across his room ending up breaking his arm. Which is finally what got him to use the toilet.
Anyways I haven't seen a movie this dark and twisted since I watched Requiem for a Dream. From what little I skimmed over the book last night, I can honestly say it's easier to understand the mother's mind set. Not to mention all of the stuff kevin does which they hardly if at all show in the movie. Especially how he was able to kill so many people using a bow, rather then a gun.
Again this movie isn't about what kevin, did but why. In that sense it's about her actions as a mother and her reflections on the past.
(Kevin wasn't wearing diapers because he liked to. He was wearing them because his mother didn't like it since she was the one forced to change him. In the book it's further explained when she talks to him about it with him in prison. She asked if he was embarrassed about it and he said no, but you were well adding "it was warm."
He then explains how some people train cat's to use boxes. They shove the cat's noses into their shit, so they use the box. Which isn't far from what you did to me. referring to how she threw him across his room, accidentally breaking his arm when she got angry at him.