We drove out to the Upper Mangatawhiri Dam on Sunday afternoon and took a couple of hours to get to Piggotts campsite. It's a pretty small patch of flat grass, so I don't know how you'd get 20 people camping there, but whatever. There's also a small hut which I haven't seen mentioned anywhere. In fact we passed by it, thinking that couldn't be the place, but quickly turned back when it became clear that it was, in fact, the place.
A thunderstorm passed over during the night. It was the first time any of us have been in a tent during a thunderstorm, so that was exciting for everyone.
The next day we got up early and hit the trail about 8:15am. Based on the warnings about central Hunua tracks being "for experienced trampers only", and that we hadn't ever hiked a long distance carrying all our gear, I wanted to give us the maximum possible time to get to Adams campsite. As it turned out even the warning-est track (Upper Mangatawhiri) was just fine. Less fine was that the Adams campsite was a lot further along the track than where my map shows it, and when we finally found it at about 3pm, it looked pretty awful. The ground was waterlogged and, while there was a sign saying "toilet", there wasn't one to be seen. We decided to skip it and push on to our final destination --- Waharau Regional Park. (Now that I've looked a bit closer online, it seems Thousand Acres campsite is a better bet ... but it's not even on my map. Lesson: use up-to-date maps and do more research!)
So our three-day tramp turned into a two-day tramp and we arrived at Waharau about 5:15pm after nine hours of tramping, covering about 18km of reasonably rugged terrain with all our gear. Everyone was tired but I'm proud of my kids for handling it very well.