You can read someone else's blog about the park here: https://bestlivingjapan.com/hanegi-park/ All the same, I thought it would be fun to document places we've been under this "out and about" heading, so that (when we leave in a few years), I have a list of things to pass onto new families.
Best attribute of Hanegi for our kids -- lots of climbing and no rules as long as you are safe. They were on top of sheds and a small house in the park. I almost had a heart attack when they were exploring new ways to climb up to a roof that involved balancing on a swinging door (!!). Other fun stuff - a giant slide, and huge rope swing, a place to build a fire, and just general running around with no rules (such a rarity in Tokyo's parks).
The only thing we couldn't figure out was how to spin a Japanese top. (like this). No matter how carefully we wound the string, we just couldn't get the wrist flick. They didn't seem interested to try and learn at home it was so hard! But, definitely would be a good non-iPad activity if they had the patience to learn.