A.C.
If you use rubber mulch chips, ask the supplier if they do any testing for heavy metals. Recycled rubber is often contaminated with lead, cadmium, mercury and other heavy metals. It is not only a risk for your children and pets, but can also contaminate the soil and groundwater. Don't get me wrong, these products have a place, I just don't believe that it is in our play areas.
Many soil and mulch yards have a rough cut "playground" mulch that has a nice loose texture. It provide a great pad and is long lasting. The key is that you need a good 6" for maximum effectiveness. Ask if they dye it...again a red dye is a red flag for cadmium.
Any organic material is going to decompose over time. The key for maintaining it is to keep it DRY. Ensure that the base site doesn't have low spots or pot holes that will hold water. Use pea or granite gravel to fill in low spots, cover with a landscape fabric and use your playground mulch. You will have a surface that helps prevent injuries and gives a quickly drying play area.