Cover to Cover

Imagine an incredibly long book, with tons and tons of main characters. The book itself starts as an illustrated children's book, following the lives of several of those main characters as children the same age as the reader, and several adult minor characters. Throughout the book, most of the characters interact with each other, but still live their own lives.
As the narrative goes on, the illustrations drop off and the writing style grows more complex, till it reaches your standard "young adult" fiction level, in which the characters are now in their early teens, and the nature of their lives changes accordingly. Each character has their own perspectives, upbringings, and view of each other character, and these mature and develop with the story.
Later, it transitions slowly to standard fiction, to deal with each of the characters' adult years, though I'm not sure how much longer it would go on from here.
I suppose it would work better practically, but not thematically, if it were a series of books. Quite a long one, with the idea being that a kid would read the series, maybe a book or two a year, for a lot of their life, with the end goal of it being to nurture a love of reading, a sense of empathy, and all that. All in all, the idea seems a little beyond me in scope. Kind of like the work of Henry Darger, but hopefully less crazy.