Who said anything about it being organised by staff. I imagine an invite to "an experience event" by a member of a club, as long as it's in the cadets own time and it's not a member of staff doing the inviting, which might get some box ticker overly excited.
We've had invites for radio and astronomy for cadets to take up if they wish, which some have, as have staff. Not cadet activities, so no need for anything from us.
If you have friendly parents with contacts who arrange something for their child and some mates ... .
I had a dad several years ago who arranged paintball other activity parties for his two sons and invited all the cadets and their parents were asked to pay for some of it. Cadets had a bloody good time into the bargain. One of his mates ran the paintball setup and gave him mates rates.