I think the OP video is hilarious, endearing, pathetic, and even touching.
I think it's perfectly fine to laugh at the performance. Just so long as when you do laugh at those kids, the last thing one should tell them is they don't have a future playing music. Puuuuhleeeze -- who the hell are you again? Only the wunderkinders can play instruments? Sheesh, man y of us folks didn't pick up an instrument (let along a stringed instrument) until we were full-grown adults. I wouldn't even ridicule that adult band. They're probably weekend warriors who never get enough time to practice together, or they're drunk or stoned... so what? The performance is painfully inept... I say that alone is what makes those videos charming. Keep plugging away dudes!