Wood products continue to breakdown, as do most organic elements, and they can break up into smaller pieces that expose spinters. Sure, splinters might hurt, yet they're not really harmful unless they are from redwood or pressure-treated wood (which is not allowed for use on playgrounds anymore, nor should it ever be used around gardens). Pressure treating wood uses chemicals such as arsenic, to minimize deterioration, which is not good inside any human (or their food!). 

Eventually, wood products turn into a fine powder that settles in the deepest area, capturing and retaining moisture, which can lead to microbes growing within it. As the intermediate layer continues to break down the larger chunks of wood into smaller shards, they crack and split, exposing splinters that can get into a little one's skin. 

There have been more than one occasions where EWF was originally selected and installed in playgrounds, only to quickly realize it wasn't such a good choice, had it removed, had a drainage system, selected the proper sub-base, installed it, and placed their 6" of rubber mulch on top of the geotextile fabric separating the sub-base from the rubber mulch safety surfacing. No more splinters, no more worries, and never having to experience what others have after many years of trying to effectively deal with the many problems of using and improperly maintaining EWF as a playgrond safety surface.