One of the best doesn't-preach-a-message, let children be who they are and do what they do kind of book. I often use this book to teach about complementary illustrations, which lay out a different narrative on their own than the one I get from the words.
Mostly this reminds me of spending time at my Grandma and Grandpa's house at the mouth of the Big Cottonwood Canyon, where we would take off down to the creek by the Old Mill for hours on end. Unsupervised play wins!
This gets five because I own multiple copies, and read it over and over again.