It's important that children start learning that when we teach them that sharing is an unqualified good in preschool, that's not the whole story. Just as when they get a bit older and learn that it isn't exactly true that you can't subtract a number from zero, they have to learn the subtleties and complexities of the world in which they live in all it's glory. Sharing is good only insofar as it doesn't distort The Market or reward people who should be punished for their economic sins (or those of their family). It is fine and admirable to share with those who already have all they need, but bad and harmful to share with those who don't have enough, as doing so would make them complacent and keep them from working hard to better their circumstances. If your friend is poor, they do not deserve ice cream until they earn it for themselves.