What was the song Kousei played after "Twinkle, Twinkle, Little Star" in episode 3? In episode 3, Kousei and a little kid play the happy piano, playing "Twinkle, Twinkle, Little Star". Kousei then changes the tune.

Was what he played a real piece of music? And if so, what was it called?
Mozart's Twelve Variations on 'Ah, vous dirai-je maman' (Twinkle Twinkle Little Star).

Listen to it on Youtube.