Awful that people have died, but I also have a hard time believing this is possible.
All other obvious evidence aside, as a 7 year old, I honestly think I would have kicked that snake's ass. Or at least made a hell of a mess resisting. I mean, I would have been in little league by that time, and although that is one powerful predator, it hasn't evolved a means of defense against a weapon. What 7 year old boy doesn't have some kind of object designed for whacking other objects in their room? That's practically all I did at that age.
I realize I'm being a little ridiculous here, but I have a very hard time believing this situation could happen. Especially in such a way where somebody would walk into the room and initially think the kids are asleep. Simply no way that a kid wouldn't put up a LOT of struggle, by snake standards. They don't generally hunt prey with self-awareness and opposable thumbs.
Again, whatever happened to these kids was awful, but I can't imagine this snake angle is even possible.
Ed. Just read Squamish's post above. This makes it even less likely. The thing didn't even hiss? Not to mention the sound of a 60 lb animal dropping 10 feet seems like it'd wake you up.