Saw the post below about play tents. We also have a couple of the playhut brand light weight foldable tents, but I found this while searching for presents for my 5 yo:
https://www.toysrus.com/product/index.jsp?productId=3906320
My boys love building forts, and this will allow the to build different kinds and use sheets. I'm hoping that it will be sturdier and larger for both boys.