298 Walton Avenue, South Orange, NJ.  Very close to Maplewood border. 

Small nice shady park, and red tubes give kids plenty of opportunity to crawl through them.  A few spaces for parking and it was pretty quiet when we went.  Less popular than Memorial Park in Maplewood, also targeted for littler kids though you could argue it is a bit more advanced (climbing wise).  Benches surround the park, so you can adjust as the sun changes position (we were there a bit)

Thanks to the maplewood/south orange message board, I was able to find this little gem. 

Had a friendly conversation with a nanny there while the boys had fun.  No bathroom close by from what I saw.  And the ballfield looks a bit worn.  See pictures below.

For more information on South Orange Parks, click this Baird website link.  For more pictures on South Orange Parks, the Patch did a pretty good job putting together their own listings, click here.  They have pretty good shots (15 photos total) of the very popular Grove Park including playground as well.