We have a large cardboard box in the living room right now (I plan on packing some toys in it) and the boys have had a lot of fun playing with it. They refer to it as their garage and they shut each other in it. I'm thinking I may just ditch the toys and keep a bunch of boxes for them!
This is Jack trying to shut James in the box....
This is Jack in the box after James had shut him in, he had much more fun being shut in than his brother
This is James trying to climb into the box with him