I know you thought hard about it, and I know you didn't and don't regard it as a child even though you use that word,
I use that word because that is exactly how I think about him. He was a child, a person, a human... and I killed him by choice because I thought that was the best option. The least amount of suffering.
Picture your newborn child with some affliction that you could not overcome. Picture your newborn child suffering in agony only to die after you have exhausted your every effort. Picture yourself helpless and impotent and responsible.
You say the procedure is "the last thing we wanted to do" and that just indicates the difficult ethical problems this entire issue involves.
The most difficult that I have ever had to face but ethical problems are personal in nature. Our ethics are a summary of the choices we make and having options restricted by legislation does not make one a more ethical person.
I don't know what to say really. I am grateful, so to speak, for having had the option of the grim choice as it was the least detestable of all. The moral calculus that brought me to that conclusion belongs to me alone. Isn't that what ethical behaviour is all about?