Were a book to be read once and never looked sat again I may agree with you but we believe that a good book is something to be treasured and savoured again and again seeing new interpretations and things previously unoticed with each pass through.
We can agree to disagree. I love to re-read books and do encourage it. But unfortunately from my perspective too many kids get the attitude that they have "been there" done that and don't re-read the books the way I would. Plus Wind in the Willows and The Hobbit get really really boring and slow at times. While they were both written as children's books, but children in the 8-12 range. All of these are excellent read out loud books in my opinion, but not ideal books to send with a 6 year old to school.
Another great chapter book for advanced readers is "Dragon Rider" by Cornelia Funkle in early elementary.
The Hobbit Grades 6-12, GLE 6th, Lexile 1000L
HP & the Sorcerer's Stone Grades 4-8 GLE 6th, Lexile 880L
The Wind and The Willows Grades 3-5 GLE 8th, Lexile 1140L
Dragon Rider Grades 3-5, GLE 4.9, Lexile 710L
How Droofus The Dragon Lost His Head Grades Grades K-2, GLE 4.9, Lexile 830L
Midnight on the Moon (Magic Tree House Chapter Book) Grades 3-5, RLE 2.1, Lexile 320L
Captain Underpants Grades 3-5, RLE 4.3, Lexile 720L
The Bad Beginning (Series of Unfortunate Events) Grades 6-8, GLE 6.1, Lexile 1010
These are from the Scholastic web site. And while these Grade Levels are designed for "average" kids. It's data to consider and think about. It is possible with some work to find books like "How Droofus The Dragon Lost His Head" that are more challenging to read yet entirely age appropriate for an advanced reader.