In article . com,
wrote:

I need 10 CY because my kids play area is 32'x16' at 6" deep.

I am advised by folks running a private school who were looking for the
best thing to put under the playground equip (the old liability scare
issues) the results of their research:

Smooth, round pea gravel. It acts in a ball-bearing fashion when kids
fall into it, cushioning the blow...they can kind of sink into it. Also
drains well if the play zone is properly designed.

It has to be fairly deep, but I don't remember how deep they said. A
Google search will probably turn up that info. Mulch compacts and turns
out to be about as hard as the ground. Same with ground-up rubber. What
you want is something that will give upon impact.

Of course, you have to contain it because it will scatter under the
little peoples' feet as they race around the area.

Dan