When sustainable building advisor Megan Lea set out to build a backyard retreat, she knew that reclaimed materials would figure prominently into the design. - Diana Budds's Backyard Retreat design collection on Dwell.
Storage for pool. looks Easy to build. believe the bottom would have more holes for water draining. Maybe staple some sort of screen inside the bottom also to keep small critters out and probably some casters or short legs to keep it off the ground.
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.