I'm in Portland Oregon at the moment, blissfully enjoying being in temperatures with two digits instead of three, so if you have a playground in the area to recommend, get in touch!
Yesterday I went to the Saturday Street Market (also open of a Sunday) and ate lunch by the Salmon Street Springs fountain, which is basically an elliptical splash pad embraced by an amphitheatre. The more I sat and watched, the more I realized how clever the design was: the form sets the splashing children at center stage and ensures that there are always being watched because all sight lines lead to the center. The splash space has jets that cycle through a series of various spray patterns and is designed so that it slopes gently towards the seating, giving the the kids several inches of water to splash in at the apex of the inner curve, which is where they spent most of their time. Too many splash pads focus just on the fountain, but neglect the puddle. We must not neglect the puddle.
And right behind the amphitheatre was a patch of sand for digging; I couldn't tell if it was intentionally placed or had been dug by the kids themselves into the fill behind the amphitheatre, which was losing its grass due to foot traffic. There were several kids happily digging away and it reminded me of
Nora Archibald Smith's 1896 advocacy of urban sand heaps...still very good advice.
(Apologies for the poor quality cell-phone photos...when I set out for lunch I didn't expect to see such a nice space!)