we've been complimented often by people like Toots that take the time to say something positive.
One thing I personally don't do is to compliment parent or child on the child's good behavior. That just seems so patronizing to me.
I will speak to the child in a friendly way about the concert itself, or any other "I'm making conversation with you" topic.
I, too, would, if I found myself running into the children during the intermission, compliment them on following my instruction. It wouldn't come across as that, nor would it seem like a lecture. I would let them know that I understand sometimes they get carried away, but that the time to do so is not during the performance. It also certainly would not come across as my correcting the parents. My tone and demeanor would translate that well. It would be something like a simple, "Thank you for being quiet after I asked. I know it can get really exciting but you did a great job after I reminded you that other people are trying to enjoy it, too." I would be talking directly to the children, with a smile to the adults. I understand that this may appear to be stepping over the line, but I do think it is an instance in which it is necessary. I know I have sometimes welcomed another adult backing me up because, after all, even at six, mother doesn't know best and someone else backing her up is all it takes to make it sink in.
I don't think you get to decide that. The person who gets to decide how it comes across is the person on the receiving end. I don't even think you have any clue how it comes across--you aren't in their head.
I firmly believe that it most certainly would come across like a lecture, especially the part I underlined.
If I were that 8yo kid, I'd hate you. You are not the boss of me. You aren't the person who gets to decide whether I did a great job or not.
If you wanted to say, "Thanks for granting my request of not talking," that would be about as far as I think you could take it. And I still wouldn't appreciate what seemed like a further change to point out how wrong I had been, and that you were the one to tell me what to do.