This, I think, is because Elly never listens to herself talk and has never really accepted the fact that as their mother, she is also their first and greatest teacher. She seems to have lived her life labouring under the illusion that a teacher is a teacher and a mother is a mother and never the twain shall meet but, as the strip where she chastises Elizabeth for having poor table manners only to turn around and Pattersnarf herself shows us, they patterned themselves after her because she was the adult they were exposed to the longest during the time their personalities were developing.
Her inability to admit that children remember what she says to them, how she says it and that it has any impact at all means that instead of seeing her as the kindly, loving, fair, and accepting figure she'd like to think she is, they rightly see her as a short-tempered, thin-skinned, angry, judgmental, biased, narrow-minded and belligerent yahoo who can't wait to find fault with everything they do and fight them at every turning. It's probably a love of chaos that makes them see her that way because the alternative is that her refusal to speak to them in any tone that isn't an angry, condescending lecture is doing something to them. This means that what happens to them as children matters and means that she's to blame and that's cruel.
What's also cruel is that anything she doesn't like about herself that they do is also her fault. It's not supposed to be her fault that they think it's okay to give up on things that don't seem to be giving her instant happiness. It's not supposed to be her fault that they don't like to help out because they see it as a punishment. It's not supposed to be her fault that the kids don't get along. It's not supposed to be her fault that they eat messily, speak English poorly, have poor study habits or any of the other bad habits they got from observing her. To accept that would be like John accepting the fact that he's a high-strung jackass screaming about his toys getting broken as a reason why Mike shies away from Daddy's Loving Workshop Of Being Threatened With Mayhem By A Belligerent Imbecile For Not Actually Having Telepathy. Admitting that they're to blame for what irritates them just ain't gonna happen.