That's really sad, and tough to deal with as the director. Have they been doing well all along this season? And this was just a bad run? It doesn't excuse the behavior, but it does explain it.
I've always used these as teachable moments. While the kids may have known what the right way to behave was - they may not have realized their behaviors were so obvious, or they may not have beeen able to control them. disappointment is always hard, but it's a life lesson they need to learn.
My first reaction would be to talk through the show with them, what went well and what needed work. And what will be improved upon next season. And then include their behavior as part of the 'things we need to work on'. I always talk with my kids about the reputation of the guard and what we want people to think about us. And the fact that most impressions are when we are off the floor rather than on. Do we help other guards out, do we cheer for everyone or talk about them? Those kinds of things. And then I talk about how that reputation can affect our placements.
Wrap it all into one. While it would be a time you want to yell loudly - I think you need to focus on this as another area for growth and development. They are kids, after all. And I'm finding that more and more parents AREN'T teaching these kinds of life lessons, making it tougher on us as instructors.