Maybe it wasn't Mom's duty to check doors and windows before they went to bed? From what I understand this was a new routine as it was Dad's first time working these hours. I can see it happening...actually I am always yelled at by hubby because I go around in the AM and open all windows however I never close them at night before I go to bed...it has always been his job to check the doors and windows.
Do we know for a fact that the door was left unlocked? Could it be possible that someone picked the lock?
Regardless of whose responsibility it was to check doors and windows- it was her first night alone without a hubby. With three little kids. And yet she left the window open and doesn't know if she closed the door? I am having issues with that part of the story.