I don't understand how some people can think that playing in the mud is somehow less worthy of a child's time than learning to read or do arithmetic. The whole point of life is to live well, fully, and with joy. Playing in a mud puddle, with the cool, smooth texture of wet earth squishing between your toes, the feel of mud as it dries on your skin, then cracks of and falls in dusty flakes to the ground... The things you can make with it, and how good it feels in your hands. The act of playing in mud is every bit as beautiful, in it's own way, as taking joy in a beautifully constructed story, or the flowing lines of a poem. People need to get past seeing the world in terms of things that are "useful" and things that are not, and start seeing it as the collection of things, events, places, people, and pursuits that make life wonderful!
I came across a comment someone had made about unschooling not possibly working, because of how you could never learn anything worthy from just playing in mud (as if!), and I just had to write down my own feelings on the topic!