My youngest turned a giant diaper shipping box into a boat last Tuesday. It sat right in the middle of the living room floor for four days. I kept tripping over the cardboard flaps every time I carried a laundry basket through to the kitchen.
I finally bought a cheap set of washable markers and threw them inside the box. I put my two older kids in there too. I told them they could draw on every single surface as long as they stayed inside the cardboard walls. It was the quietest twenty minutes of my entire week.
They covered the inside with red and blue scribbles and something that was supposed to be a map of our street. The markers bled through the bottom a little bit. It stained a tiny patch of the rug under the coffee table. I just moved the table over an inch to cover it up.
The box eventually lost its shape because my middle child tried to sit on the side panels. We broke it down and shoved it into the recycling bin on Sunday night.
If you get a large delivery box, do not break it down immediately. Give them washable markers and walk away. Just make sure you put an old towel under the cardboard first so the ink does not ruin your floor.