The sand is reasonably clean but you can find some pretty nasty stuff if you look closely, trust me. I've sifted through it while playing in the park and it's got lots of cigarette butts and other detritus mixed in. However, the kids love it, and mine have been playing there for almost 7 kid-years with no ill effects (except for that twitch, must get it checked out :p ). Taking away something that so many kids enjoy so much because it seems "unsanitary" without any evidence at all of a health problem seems like a dumb, CYA maneuver designed to remove the whiff of risk from kids' lives (while providing them with a play structure to risk their necks on, but I digress...). I don't know about your kids, but mine are far from sanitary to begin with.

For more on this kind of kid risk-avoidance parenting groupthink, have a look here (http://freerangekids.wordpress.com/).