I'm so sorry that you encountered this. I can just imagine how you felt with that response. What a sorry excuse, but as a parent, my parenting obligations were never on vacation and children's behaviors should never be on vacation.
I am appalled that RCI did NOTHING to stop this behavior! This has me very concerned as I will be traveling 4/7 thru 4/21 on their new Radiance of the Seas, and I can tell you that I'll find the captain or be in someone's "space" if the children become unruly!
This will be a 10 year + dream come true to go on this cruise and I'll be sadly disappointed if it is ruined because parents can't control their children.
If RCI isn't going to control the number of children who come on board, they should certainly take charge when it is obvious that the parents aren't going to do anything about it!