Pianist age 4 plays "Mary had a Little Lamb"
We've shown Mary had a Little Lamb before, on flute, but of course it sounds very different on piano. People are often surprised to learn that although the piano has strings, it's actually classifed as a percussion instrument. But percussion basically means "instruments that make their sound when you hit them," and that's what's happening here: when you press the piano keys, they operate hammers inside the piano, which hit the strings and bounce off again.
So an important skill for pianists is learning to touch the keys with enough strength for those hammers to produce a sound - but not so much that the sound is harsh. Although he's so young, you can see (and hear) that this young man is already doing an excellent job using the weight of his arm to drop his fingers into the keys, producing a round, ringing sound.
You probably already know that words to this song! But just in case: