When I was a young mother of two boys under 2 (years before our third guy surprised us), I became suicidal. It was a hard time, a scary time. It built to a crescendo in my mind shortly after a new diagnosis in our second child.
When your mind tricks you into feeling as though you aren't good enough, that your kids would be better off without you, it becomes its own mantra.
Kudos to you for the courage to write about it.