If "quite risky and challenging activities take place." then I think it would be in everyones' best interests for parents to keep a close eye on their own children, instead of leaving it up to a handful of vetted playworkers. I take my nephew to the park, and I need eyes in the back of my head just to stop him doing something stupid, like leap off the slide. I certainly wouldn't trust someone to be looking after an indeterminate amount of children, for unstructured play, in a place deemed "quite risky".
Although, I bet there is more to this story than meets the eye (as with most news stories).
I would like to hear from someone local as well. I'd like to know if parents are not allowed to watch from the other side of the fence (unless it's a big fence) as the article suggests, because (if I remember from my days as a young child) parents aren't allowed to roam around Softplay willy nilly, they have to sit on the sidelines, but they can still watch IYSWIM.