Dahl makes it clear as the novel opens that he believes that most parents have distorted and unrealistic ideas about their children. But between the two extremes of distortion that he perceives, which are overvaluing and undervaluing children, he believes it is much, much better for parents to think more highly of their children than they deserve than to ignore or belittle them.
Dahl believes parents should think highly of their children but should keep such feelings to themselves rather than bragging about how great their children are, which he finds a "disgusting" way to behave. Nevertheless, given a choice, it is better to brag than to belittle.
What makes Matilda's parents, the Wormwoods, so terrible, is the way they ignore and devalue their very talented and sensitive young daughter. In fact, they find her talents, such as her ability and desire to read books, a bother. She annoys them because she is intelligent, and they would rather get rid of her than pay attention to her.
Because her biological parents are so terrible to her, Matilda finds a new parent in her teacher, Miss Honey. Miss Honey models the way a proper parent treats a child. She perceives Matilda's intelligence, compassion, and sensitivity and honors those traits rather than seeing them as weaknesses. She treats Matilda with the respect that a parent should rightfully afford a child and so earns the role of the replacement parent to this talented and deserving girl.
I agree with Dahl that parents should treat children with respect. I agree, too, that if parents have to go to excess, it is far better to overvalue children than to ignore and criticize them.