To be generous, what this meant is either that you were below the reading level for the book or you misunderstand the core skill of reading and using style in the English language. Reading and understanding when rules are broken leads to knowing when they can be. We don't skip Shakespeare because the language is funny and archaic. Reading these authors is both a part of style and content literacy for the English language. Disclaimer: I'm not comparing them.
There is a difference between understanding a book’s contents and being able to read the book without having it rewrite your understanding of the English language such that you have no idea what is correct and incorrect because your grasp on that was tenuous in the first place. Children are expected to avoid being rewritten at stages where they are extremely impressionable and are easily rewritten and then they are blamed for it. It is fairly sadistic thing to do to children.
No, it's all a part of learning to read and understand language.
If a child is having that much trouble with it, which would be unusual at grade-level, then the book is above their level. At that point, the child should probably be screened for a delay.
How this generally works is that young people ingest these books, and by doing so their language ability increases to be able to flexibly understand (and use, if stylistically appropriate), non-standard grammatical forms.
