So today I took a friends' advice and dug a grand hole in the yard with my son. Our yard has limited toddler fun resources, but lots of space. It was about 50 degrees - warm for lately. It took about 15 minutes of me digging and playing before he really got it, but then he didn't want to stop. We had sweetgum-tree-stickerball-people, shelters made from tree bark, flags made from leaves, and lots and lots of sticks in the damp earth. All eventually got whacked with a plastic shovel, but who cares. AND we got really dirty. Which is tricky to accomplish in the winter.
And here's what the boy's room looks like at the moment. It is forever a work in progress.