I read The Book of Three by Lloyd Alexander to my first two boys when they were quite young. It is heroic fantasy, the first in a series of five, and both of them loved it. I have been looking forward ever since to reading it to grandchildren as well. Reading chapter books to grandchildren is different* (not nightly), reading to girls is different, and reading to each child is different. Still, I am a touch disappointed that she is not taking to it as well. Right from the first chapter I could sense she was not entering into it with the same verve as her father did - he leaped about the room slashing with swords. We are just now getting to Eilonwy, and I hope this perks things up for her.
There is a flaw in the writing which I had never noticed before, which tells me something about fiction in general, and I would not have noticed if I weren't analysing what is happening. It tells me first that if the narrative pull is strong enough, flaws in writing get overlooked, which might be some encouragement to fiction writers out there. When the adventure is happening, weaknesses are not noticed; when the adventure is not working, even small problems become magnified.
Too many characters are introduced too quickly. It's hard to keep track of unless your imagination goes there to live.
We have some things working against us. While there are many girls who like heroic fantasy and adventure, I think the taste is stronger in boys. Part of J K Rowling's more universal appeal comes from her combining the genre of heroic fantasy with that of the "school story," a genre more popular in England than America. Notice that Lewis's Narnian Chronicles have a touch of the school story in them as well, in that a mixed group is the focus, and initial events are structured around school holidays. There is the interrupted rather than nightly reading, as mentioned above. Emily is a reader, but her play time is around American Girl and about a third of the Disney Princesses, so half her reading goes there as well. Her mother was a reader of Anne of Green Gables and Little House books, and Emily is much like her. (We'll see about Sarah and Aurora, four years younger not quite that way.)
There was less heroic fantasy available to read to children years ago. When we were in college in the early 70's my wife and I read just about everything in the fantasy genre which was in print. This was just as Sword & Sorcery books were taking off - eventually whole sections of bookstores would be devoted to that - but there wasn't that much then. I think we were less fussy, and the implied excitement of "there aren't going to be many of these" may have crept into my reading. Eventually there were so many Redwalls and Xanths that they wore out even Ben.
In The Book of Three, We are introduced to Taran and Coll on page 3, Dallben on 5, Math is mentioned on page 6, Gwydion, Arawn, and a few historical names on 7, The Horned King on 8, and Hen Wen on 10 - this on pages of about 250 words each. Half of these drop out of the story for the time being, while The Horned King's troops, Melyngar, Gurgi, Gwythaints, the Cauldron-Born, and Achren pop in. Medwyn and Gwyn the Hunter are mentioned. That's a lot for a third-grade girl who is only getting into this story once a week. How to know who is important and who is secondary? We are just about to get to Eilonwy, then Fflewddur Fflam, though these are at least going to come in more slowly, with proper introductions. After that there are a few new characters per book and it isn't so dizzying.
Contrast this to The Hobbit, where there are many dwarves immediately joining Bilbo and Gandalf, but these are essential Thorin and Lotsa Dwarves, who only differentiate over the course of the story, or not at all. The Lion, The Witch, and the Wardrobe introduces two characters right in the title, then the Professor and four children, but they are rather just a sibling-group until Lucy goes into the wardrobe, and meets Mr. Tumnus, and later, hears about the White Witch. Redwall spends an Introduction on the villain and his nameless comrades, then introduces a few mice in the first chapter.
I had a similar experience long ago, reading to her father. I had loved Susan Cooper's The Dark Is Rising series but found they did not read well aloud. I am no longer sure why, but I think it may be as above - the plotting is skillful, but the narration less so. Or perhaps the conversation was not quite natural - that bother's me more than others, I think. I have not reread them since. My brother countered that as they were not made to be read aloud, what I see as a failing might actually be a positive for one reading silently. This could be so. Update: We have a notebook of everything we read aloud to both boys and I read my notes for The Dark Is Rising. What I disliked then was "things happen out of the blue, motivations are inadequate, symbolism is unclear." There is also an anti-Christian part I had forgotten, and the book scared him (he was six).
The opposite happened with Watership Down, which I started reading aloud with trepidation because of its length. Jonathan had loved Rabbit Hill and The Tough Winter, so I thought rabbits might continue to hold him. WD reads aloud very well, despite all the ground-level view of plants. The characters are clearly differentiated, so a child can follow them. He loved the book, which put it on the list for the Benjamin, who became obsessed with it three years later.
Well, at least I got one thing right in my not-very-good 100,000-word postapocalyptic novel. I only introduced one character in the first chapter, then the others one or two at a time per chapter.
*"Not nightly" is huge in and of itself. It means The Best Christmas Pageant Ever has to be started mid-November. It puts Lord of the Rings aloud completely out of reach, which is sad because it was central to her father's and uncle's evenings growing up. It took months at a half-hour a night, so intermittent reading would go beyond a year. I might hope for The Hobbit. We'll see.