A cardboard box is a happy thing, and the bigger the better. It’s not every day you buy a new fridge or washing machine but you can usually pick up a box from places that sell large white goods. A box can become a house or fortress with a little imagination and some rough cutting to form doors, window and parapets. A serrated knife will work better than scissors. Even if you only manage a few large sheets of cardboard you can construct a small space kids will want to play in. You will need to take charge of the knife but let kids direct the design. And they will enjoy decorating the place inside and out with water-based paint.