The Bobbsey Twins! I loved them as a child.
I have a 42’ hallway going into the library, where the hallway is floor to ceiling bookshelves on both sides. Two of the bedrooms are also filled with bookshelves, and the library closet holds all the boxes of books that don’t fit on the shelves. The Bobbsey Twins sit in the nearest bay to the library, right above the shelf of Little Golden Books and right next to the Classics books from U of Chicago. Flossie and Freddy and Nan and Bert! Sold for $1 each and a stack of them was the BEST Christmas present EVER.