Use tension rods and a sheet to make a tent in the hallway for the kids. You can decorate the sheet with fabric paint or markers. And can be easily stored when done. this is awesome I think grandma needs some tension rods
How to keep a child busy for hours in the summer: DIY: Giant Ice Cube Awesomeness - filled with plastic animals, dinos, and such. And I'm sure you could put in food dye before its frozen to color it like the ice block in the photo.