Congratulations, Hajime. You have popped the center pole back. It's still going to squeak a bit because of rust, but at least it's less likely to wobble. ... Unless he takes care of whatever that big dent where a child would sit, too.

Looking around, there doesn't seem to be anything directly related, but the tree closest to the merry go round has a few yellow threads caught in the bark, like someone was leaning up against it.