My kids have always enjoyed seeing the possibilities in a huge cardboard box. They use the boxes for forts, castles, firehouses, hideouts, and submarines until the boxes no longer resemble rectangles.
We haven't had a box for a while, so Little Brother was happy when a 4-foot-high box came into the house last week. He immediately claimed it, and today Big Brother used his Brand-New Big Honking Camping Knife to cut peepholes, a window and a door into the box.
I asked Little Brother if he was going to decorate his new clubhouse. "No way," he told me. "If I do that, everyone will know it's me in there."