@PeteS in CA I failed to find specific fire codes in PA for daycare centers, but it seems for most facilities in PA, the requirement is one smoke detector for every floor. Also, this daycare was operated out of an old house. If I remember correctly, smoke detector and carbon monoxide detectors are required in PA for new construction, but not for old homes. Since this was a business presumably licensed in PA though, I would say residential requirements don't apply here.
One of the news stories said there were numerous extension cords running underneath the carpet in the living room. I'm reasonably sure that's a code violation too.
Presumably, the place had been inspected regularly. if that's so, I would say your guess that the inspector fell down on the job is likely correct.
I hear that a state lawmaker is calling for an investigation into how this facility passed inspection. When I find a link to a news article on this subject, I'll post it.