From Joyous Music School in Long Island, New York, this is perhaps the youngest string quartet ever: The Joyous String Quartet. Above, they perform Katy Perry’s Firework. Below, from Nikolai Rimsky-Korsakov‘s The Tale of Tsar Saltan, the quartet performs Flight of Bumblebee:
Update: Their version of Summer (Presto) was removed from YouTube.
Bonus vid: How playing an instrument benefits your brain.