We have done La Nouba, fireworks cruise, dinner at V&A, parasailing and spa treatments with our adult children and the "kids" loved La Nouba better than any of the other special things we have done. In fact, DS26 was the victim selected from the audience to participate in a stunt on stage. All of them have said that would definitely see that show again.
Another thing we have done was arrange a type of scavenger hunt through MK through the company, Gifts of a Lifetime. Everyone had a blast with that too.