We can go back and forth on what these parents should have done (and I know I've indulged in this quite a bit in this forum so, no shade to anyone doing this) but I don't believe it'll be productive, clue-wise. The fact is, a good portion of kids are just not properly cared for by basic welfare standards; that's the sad reality. Maybe this is a typical weekend routine for them.
What I have been dying to know is whether they often let themselves out to play. The mom does go out of her way in the interview to say they're not allowed to do that and they're *always* supervised outside, so this suggests not. If not, then why assume this is what happened?