The City where my son lives installed rubber mulch in the play area of the local park. I like it. Cleaner & safer than wood chips (no slivers) and better impact absorption than sand or organic mulches. Judging by its appearance so far, it looks like that rubber mulch will last quite a while too... so greatly reduced risk of injury, and relatively maintenance free (other than having to occasionally rake it back in from the surrounding area).
The only downside I can see is the risk to very small children, who may put the rubber pieces in their mouth.