Intelligent teenagers will view it as what it is: a show, not an instruction manual. Sheeple teens who will start twerking at school because they saw Miley doing it on stage... well... maybe they should just stay at home. Permanently. I mean, god knows what would happen if they went to the circus

.
As for pre-teen children, clearly they shouldn't be going to a live music act alone, so... don't take them if you don't want them to see it?
I'd have no problem with my teenagers seeing these shows. I have no problem with my 4 year old watching her. She has constant social commentary from us and so she'll be more than able to put acts like this into context.
Well... I say no problem. I'd be a LITTLE concerned, because Miley's music is pish. I'd be like "are... are you sure? Are you sure you want to pay actual money to listen to this cacophony? Well... ok... on your ears be it...".