If you understand and agree that twaddle (a word used by Charlotte Mason to describe books that are not enriching) is not what you want your children to feast upon, how should you proceed?
One of the first things I did (and I do again from time to time), it's to clean my home from twaddle. I go through the shelves and pick books that I don't need to have as if I were cleaning my pantry from junk food. I don't do this to perfection. If you came to my home you'd see books that are not that worthy. But my home is not a PNEU school, and my pantry is not a whole food store. The idea is to get better, not to be perfect.
What do you do when you visit the library? We want our children to develop appreciation and autonomy when we visit the library. So this is what I do. I let them look at the books they like, and I check what they get. (Same as when we do our grocery shopping). I don't let them take ANYTHING they want just because we don't pay for the books. If it's a book that goes against our principles (we don't celebrate Halloween, for example), they have to leave it there where they found it. As for these books that catch their attention but that are twaddle as its best such as Care Bears, Barbie, Scooby Doo books, etc. I've sometimes let them come home with some of them, but I DON'T READ THEM. I do not read anything that bores me, that irritates me, that doesn't enrich. With this said, I sometimes read innocuous twaddle the same we sometimes eat something not that super healthy, but that's not our regular spiritual, intellectual, or physical diet.
With time and realizing that the books I offer them are far better than those they've picked sometimes, my daughters have started to choose from the library some books we've read before and come to love. They are also finding their treasures themselves. And I sometimes come home with several books I think will be worth to find that some aren't, so I stop reading those and return them. I guess I'll be able to say more of how we do this when they can read, but I know there will always be some guiding and censoring from my part. The same we wouldn't watch any movie, or we wouldn't buy any junk they fancy at the store, or we wouldn't wear any clothes.
Finally what to do when they don't read yet, and how to start them in chapter books. There is no more value in chapter books than in non chapter books. The value is in the type of book you are reading. You want your preschooler to be exposed to good quality literature, if it's a book without pictures that is worth but it's over their head, there is no point in reading it to them. For the longest (for my perception) time, my oldest daughter wasn't ready for readings that were not shorter and with some picture support, so I didn't read any of those. Still to this day, I read things that are at their LEARNING CURVE level (that present a challenge, but are not over their heads), and that are wholesome readings, and things at their COMFORT ZONE. Since they are different ages I read to each of them separately, which delights the youngest and challenges the oldest, and to both together, which challenges the youngest one and delights the older. We do a lot of nursery rhymes, simple but rich picture books, more elaborated picture books, and some of the good and simple chapter books such as Arnold Lobel (Mouse Soup's author), Hoban books (Frances), Frog and Toad, Amelia Bedelia books, Little Bear. We also do our own trial and error, that's to me the FUN. To be wholesome book hunters.
CM didn't think it was that necessary to read lots of books to young children. The principle that less is more is very applicable. Lots of picture books (specially the twaddle type) are in a sense like TV, they stimulate their vision without enriching and engaging their minds. Children literature has grown and improved since CM times too, but the fact that our children need more outdoors and less bookish time is still a truth to me. And do not forget about telling them stories with your words, help them paint a mental picture of what you are narrating. Their attention will develop with observing nature outdoors, their vocabulary will grow with your telling stories, their minds will be engaged in ideas with exposure to a few wholesome books, and they will transition to "chapter books". But at this stage, enjoy the joy of those priceless children books and nursery rhymes that delight us the most. If you look at the free readings of Ambleside Online Year 1, recommended for when they are 6 or 7, the selection is of wholesome chapter books such as Little House in the Big Woods, some of which can have delightful illustrations, as Pinocchio, and for Year 0 go to their list too to find quite a long list of wholesome books.