lean on your parks & rec person for the standards they follow. As you can imagine, there are national and regional ones, likely local too. There's an ATSM, and a number of organizations - as well as certified playground safety inspectors that have to sign-off on projects (and who sometimes have to come back & re-certify projects on a regular basis). That's why so much playground stuff is off the shelf. Playground people don't want the liability of inventing new stuff - they play with the context, not the content.

Don't go down the rabbit hole until you have a real sense of what will be required - and if it needs to be you to do so. Maybe the artist can be that context person and actual play elements are under someone else's purview. Also, when I did a playground project with an artist, I actually recommended he speak with an attorney about his potential liability. Most standard agreements don't relinquish artists fully from liability after the project is completed and accepted, and their engineer is also on the hook if one is engaged. Lots to think about.