>>6534507except a communist would let b keep the flute, assuming of course this is occuring under communism. If not then child b didnt actually make the flute, she exploited someone else to make it. But assuming we have already gotten to collective ownership of the means of production the flue b makes with hew own labor belongs to b. If she was a worker at a flue factory and made it during her working hours then she would still have to buy it with exactly one flutes worth of labor. But assuming she made it as a hobby in her spare time its her flute.
A would already have a flute if she was being trained as state flute player, or be able to purchase a flute with exactly one flute worth of labor based on whatever she does.
C does not exist in socialism, and is roughly equivalent to child A and B apart from the flute issue.