This is a great idea for those of us who have a "broken" birdbath (no longer holds water). I would be careful, though, to place it somewhere where it would be protected from extreme weather because one big storm and it would be ruined.
A Dry river bed instead of a traditional sand pit. Large and smaller river rock lining a sand river with tree stumps, ferns and toys. This is a home daycare that has a lot of natural play elements in their backyard play environment.