There was an awful story a while back of a poor little girl (toddler age) who died after being left alone for several days on end while her young mother went out partying. She was estranged from her family after running away as a teenager.
I think it was NYE and then her 21st birthday or something similar, so she felt entitled to do go to several parties without returning home in between, leaving some food out for her child, who was far too young to be able to feed and toilet herself properly anyway. She treated her baby as though it were a cat. Food and water left out, telly on for company, what's the problem?
No-one noticed that she was gone or heard the poor child cry. It was an assisted living type place for vulnerable young mothers and there was a staffed office, yet no-one noticed that she went out without the child and didn't return for days.
When the case came to court she was seen on CCTV leaving and then returning home to find the child dead.
People are too often scared to ask questions for fear of being told they are nosey or meddling, especially if it turns out they are wrong and there was a babysitter there all along. But if your gut is telling you to make some checks then knock on the door and bloody well check. Make up an excuse if need be, but check.