As short as it was, somehow I missed the "busy" word in the description and thought the parents are not a part of the world of living anymore. It's kind of goofy they are merely busy, though of course realistic. In real life, in a developed country, a high school kid likely wouldn't be left to take care of kindergarten-aged siblings on his own. But this is manga, not real life, so I was expecting that, having missed the word. The situation doesn't really have much gravity when the parents are just momentarily too busy. If they are permanently too busy to look after their own children, they are kind of irresponsible parents.