I have a question/possible scenario. Kids were in the living room right?
Lets say son and dad were in the other room, but kids were sleeping right next to each other. Could the snake have gotten into the room, and looking for something warm, laid on the kids? That's a big animal (100lbs right?) and 100lbs of muscle on a 5 and 7 year old, especially if it managed to get right on their chests/windpipe. If there were any broken bones, or trauma, they could have gone into shock before being able to do anything or scream... and hard to scream if a big snake is on your windpipe. Death throes/panic could have frightened the snake and caused it to defensive bite. It wouldn't need to constrict to cause asphyxiation on two kids that size.
It'd still be the snake who killed them, but freak accident and utterly the fault of the owner for having the snake in something it could get out off, especially if it's happened before.