I'm a librarian who loves anime, manga, and reading a wide variety of genres.
"'You know, though, Molly, that Dave and I count on you and Michael to take care of Heather. It's up to you to make sure she doesn't run wild in the woods all day.'"
OMG, I hate these parents. The mom seems to know that Heather hates everyone in the family except Dave, her dad, so she must know that all of Heather's claims about how mean Molly and Michael are to her are lies. And she still makes the bulk of the work involved in watching out for Heather Molly and Michael's responsibility. If something happens to Heather, you know they're going to blame the 12- and 10-year old they told to watch the 7-year old, instead of thinking "Hey, maybe us adults could have switched off between working on our art and actually watching out for our kids."