We have a rule in our house. No cardboard boxes are to be recycled until they are covered in crayon, marker, paint and scotch tape, and at least 6 windows/port holes/secret doors are cut into the sides, and the entire structure has been sat on, jumped on, rolled in, rolled over, rolled up and otherwise mashed into a giant, limp wad. Well, to be fair, this is not a rule as much as a precedent that is followed with great rigor and passion. Also, I let the kids play with them, too.