This video was posted six months ago, and this is the first mention of it I've seen here. What a cool opportunity for the kids. A couple of them even pay excitedly in the comments section.
That being said, the effect on Brian's voice is...unique. Is his voice being doubled live, as he's singing? Or was it added later? Not asking sarcastically, I genuinely don't know.
I don't think the whole thing is meant to be live per se. Brian is doubled and processed heavily beyond doubt.