Don't know what the rules are in NZ or care less but as for Australia I have done simular years ago before cost sharing was allowed even on a number of occasions.
Years ago we had an annual "Flight day at Parafield" for my sons scout group. We would have a picnic lunch right under the tower and I would fire up my trusty Cherokee 180 and take 3 at a time on a joy flight over Adelaides northern suburbs. Usually the Tower would even let the kids up to have a look at the operations. The scout group would charge a nominal fee for the day as I fund raiser (not that I would see any of it or expected to) and all the kids enjoyed a good day out. As I said so good we made it an annual event.
I have also on occasions donated "joy rides" as a raffle prize to good causes. So long as the passengers are made aware it is a private flight it is quite legal. If it wasn't do you think the controllers in the tower would have not passed my name along to the relevant authorities let alone been party to it?
Some of you guys need to get a life.
What do you think will be gained by raising "mystery grey areas"? Have you ever read an insurance policy? Are you that jealous that your not included in doing the flying? Or do you think by whinging about it these kids are going to run across to some charter company and pay top dollar to do the same thing? They won't they just won't get to go period.
CASA aren't interested in such petty matters. What they are interested in is blatant rorts of the regs,as they should be. Such as conducting unofficial charters to events for hire and reward.