Rainbow Large Round Wall Clock by Art is Everything - $49
Great for girl's room.
Paint on inside of wall cubes...
Area rug color
Bug & flower display - do with corkboard?
Metal nightstands/side tables/other storage for DS' room would work well with theme (beware of sharp corners though...)
Spice racks from IKEA used as book shelves. Could use beside kura bed.
giant flowers and pom poms
mattresses with lots of cushions for secret passage?
desk against shelving - possibility for corner of room if enough space?