We're only 4 days in, so we can make some changes. I highly doubt anyone has read a 600 page book, yet. And if you have, I'm jealous. Where do you find the time?
#1 - Instead of 600 page book for the 25 points, it only needs to be 550 pages.
#2 - Children's books, in order to count for full points, need to be at least 100 pages long. For easy readers and such that are shorter than 100 pages, but longer than a picture book, we've decided that we'll give .5 points for each of those. So ten pictures books to get 1 point and two easy reader books to get 1 point.
Oh, and one book counts for one category even if it could fit into multiple categories. No double-counting a book. (Not even if you read it twice!)