Reading is "it" now; Madeleine's favorite activity. This particular picture was taken immediately following a trip to the library. Her nose was stuck in the book from the second the van door closed to later that evening, managing to walk inside upon arriving home without losing her stride.
What's interesting about this development is that I remember doing that as a child. A lot. I remember losing myself to the outside world and not hearing ninety percent of what was going on around me if I was fully absorbed with a book, which I often was. And now Madeleine is the same way, lost in a book and unable to see or hear the world around her.
Don't you just want to jump in after her and see what's so interesting?