I spent another hour at the playground today, it was hot and sunny and no kids around. Once again a I removed lots of chain-link fence wire - possibly from an earlier playground? This one was set up only recently.
I found a large coin that at first I thought was a silver dollar but on closer inspection it had Chinese writing on it:
I looked it up and it is a 2013 Taiwanese 10 New Dollar coin. Apparently the writing says: "The country flourishes and the people are living in peace". It's worth less than $1US. Here's what it looks like clean (thanks to numismata.com).