I'm a cheerleader for CHILD'S PLAY...with a particular fondness for cardboard boxes. Small ones, big ones, and the oh-so-perfect medium-sized ones.
To me, cardboard boxes are more than just corrugated cubes, and the carriers of something new, or basement storage... they are the gateway, the threshold, the precipice (!) to child discovery and imagination. (Warned you about the cheerleader part.)
All of my children's books advocate good-old-fashion PLAY. Sans technology. Simple-simple-simple. Princesses and Super Heroes play inside/outside to their hearts glee. In Do Super Heroes Have Teddy Bears? , brother and sister design/build a super sonic rocket ship from a few unsuspecting containers. Play. Even when things get dramatic. Play. It is the precursor to creativity.
(See Washington Post article on the importance of play.)
Give a kid some tape, boxes, crayons and scissors (the kid-safe variety) and let 'em roll. Before lunchtime you will have, in your living room, a submarine WITH sonar, or a dinosaur museum for T-Rex and Stegasaurus, or a really awesome time machine, or grocery store. Add some pulleys and string, and you'll have an elevator. It's practically guaranteed. 3D at it's finest.
Cardboard boxes ease the hard edges in a person, and make them more rounded. Bring on the blankies, and those boxes become a quiet haven, with sky lights, for gazing at books.
Granted, the little ones may need help getting things started, but once they glimpse a newly constructed pirate ship... they'll become cheerleaders for cardboard too. "Arrgghh-Argh-Argh," I mean, "Rah-Rah-Rah." There's simply no limit to the play potential.
Handspun cities are untidy and cumbersome, but trust me, your dining room will one day, soon, be a dining room again. And you will, one day, miss the busy cardboard metropolis... and ESPECIALLY you'll miss it's co-creators.
(Nick was the king of cardboard at our house on E Warren Place. Here, at age six, he had just completed the finishing touches on his Sea Hunter. Yep, 'caught many a shark and eel with that contraption.)