been looking for something like this for a long time
Is sounds like a cartoon short I see long ago.
It was about a boy that finds a green caterpillar, and the boy played a Harmonica and the caterpillar did something? I remember there being a commercial in the cartoon for caterpillar LP’s and most memorable, a commercial for caterpillar toothpaste.
At the end there about to perform on stage and the caterpillar is missing. Every one looks for it, and in the end the caterpillar turns in to a butterfly.
Have been looking for it for a long time.