We know that, in an emergency, JB doesn't mind admitting to having left children alone. That's how she staged this whole thing.
So why, if she came home to a missing or dead child, would she hide it and take care of it herself and then stage a fake scene that involved the same detail of leaving a child alone?
I'm not seeing anything, personally, to indicate accident.
Not 'picking sides' at all. Just explaining my experience with what can happen to small children when they are left alone in residences for extended periods of time.