It's obviously child A. Aristotle's notion of telios. Everything has a purpose and it is immoral to deprive it of its destiny. The purpose of a flute is to make music and if it is the best flute, it belongs in the hands of the best musician, so the world is then filled with the best music and the musicians and the flutes purpose is fulfilled.
To give it to child b would only feed greed and purposeless possession.
To give it to child c, is to create a society full of mediocrity and to deprive that child from seeking their own destiny.