Karen, I was thinking that something that might help your son get through this horrible tragedy and profound loss, and maybe ease just a bit of his pain, is to let him know just how common what happened actually is (we must get at least one person a month posting here because they lost their bird this way), and to let him know that our Community/forum here is extremely active with who knows how many people trolling-through without registering, and that the loss that he and your entire family is feeling right now is actually going to help educate many, many others who are reading this post...
Many of our Community's long-time members have years and years of experience having birds as a part of their lives and their families, but the fact of the matter is that the average person who owns a pet bird has ZERO experience with birds, and the bird they have in their lives while they are reading this thread is their very first pet bird. So the average person reading this thread, who walked into Petco or Petsmart to get a fish or a hamster or some other type of pet, and who walked-out with a baby Budgie, Green Cheek, Cockatiel, Sun, or Jenday, has absolutely NO IDEA what the hell they are doing or what they've gotten themselves into (and you know this is going to be a popular thread, as sad and macabre as it is, we all know that people read the threads with a subject/title that mentions "tragedy", "loss", "accident", etc. first, before reading any other threads)...
***So the bottom-line is that the thousands of uneducated and inexperienced new bird owners who are going to be reading this thread, from now into the distant-future, and who will hear your story and feel your son's pain, their innocent, sweet pet birds are the ones who your son's story is going to save!!! I can see exactly how unaware and inexperienced bird owners reading this thread are going to react to it: "Damn, it never crossed my mind that I could kill him this way", and "Oh my God, we've gotta stop sleeping with her like we've been doing...Boy did we get lucky. She's going to be mad sleeping in her cage but she's just going to have to get over it!"...
So I just hope that your son realizes that the horrible loss and pain that he is going through is going to save the lives of thousands of other pet birds all over the world...And maybe knowing this will give him just a little bit of comfort...