In a short video, she explains the "fill the page theory" that the entire site is based on. It's a really neat to site and also has a facebook page!! You can search for "little stories" on facebook to find the fb page and stay connected there.
Her, "fill the page theory" emphasizes that kids need to have multiple experiences with the same word. They need to know that balls are not just one kind, but come in many sizes, colors, have many uses, are found in many areas, etc. What a great name for a concept that is so important!