I love the idea of narrow shelves with 'safety' rails for storing and displaying kids' picture books. The effect is so inviting; kids would surely be drawn to it. -- Unexpected Storage for Small Spaces: Apartment Therapy.
Great idea RE the twin mattresses. I also love the tree pictures on the wall! Love to display kid-made art in a kids room! Two twin mattresses, some plywood, and a great playroom that doubles as a guest room or sleepover room.