Feral Heart Library! (Book Recommendations Needed!)

[PocketMutt]

I would think The Plague Dogs to be mature, as well as Watership down. Perhaps for both the graphic material, subject matter and difficult comprehension. (I have read both books, and I would prefer them to be labelled as mature as they are not books for everyone.)

The Tale of Despereaux by Kate DiCamillo
Call of the Wild by Jack London
Black Beauty by Anna Sewell ! (sad content)
Misty of Chincoteague by Marguerite Henry
Stormy, Misty's Foal by Marguerite Henry
Sea Star: Orphan of Chincoteague by Marguerite Henry
The Island Stallion and The Black Stallion by Walter Farely
Starshine Legacy (the comics) by Pixel Tales and Hidden Entertainment (possibly?) ! (scary content)
Wolf Children by Mamoru Hosoda ! (sad content)
(M) Ginga Series by Yoshihiro Takahashi

You're absolutely right- sorry about that ! I never read the books myself and had heard they were pretty infamous for being dark but I also saw that somewhere they were considered children's books. However, I'll definitely listen to your advice and label them as mature ! Thank you !
As for the rest of your list- they've been added. Thanks again !