I'd personally go with natural grass. Sand attracts cats (or perhaps other little creatures) to use it as a potty to great for the kits. Otherwise, I might select a rubber mulch which will fade over time yet little creatures will be less likely to use it as a potty. If the kids are not terribly young pea gravel would be another option.

Grass does not meet safety guidelines for playsets. Dirt can compact as hard as concrete in traffic areas. A few summers ago a neighbor boy fractured his arm dropping from our monkey bars onto our lawn. It was awful and sent me into in-depth research on this subject.

Here are guidelines for home playground safety:

https://www.cpsc.gov//PageFiles/122146/324.pdf

If you call to get a quote for playground chips you are probably going to gasp. Surface material and containment can cost as much as the playset itself. We had to have a 50' cedar tree removed from our front yard last year so we just had them leave the chips and we use that for surface material. It's far from perfect, but it does the job and it was free. You might be able to get free cedar wood chips by using Chip Drop https://getchipdrop.com/

I encourage folks to not invest in those wood playsets. My best friend bought a Rainbow set around the same time we bought this metal Lifetime Monkey Adventure Playset from Home Depot. Her Rainbow set looks awful and requires maintenance, ours looks brand new and we've never done anything to it. We regularly have 5-6 kids on it at one time, so it's neighborhood friends approved.

Finally, one more piece of unsolicited advice... get an umbrella insurance policy if you don't already have one. Attractive nuisance liability is a cause for concern.

benjesbride - Thanks for the info on chipdrop!!! Well organized and professional site. Thanks. April