In practice, the oranges are good for our health. If you consume of the season give us the maximum of nutrients. Furthermore, their season coincides with the winter then also one in which we are more prone to the famous seasonal ailments.
There are several studies that demonstrate the effectiveness of this fruit but squeezing, or rather the way in which the orange juice is discussed. There are those who do not care and just squeezes with a commercial juicer. There are those who instead argues that the oranges should be pressed manually with only plastic juicer.
This theory predicts that the oranges never touch the metal so even the knives to cut should be plastic to not "break" vitamins. There is nothing shown of course. The only factor affecting vitamin C is air. In fact, it is recommended to drink the juice as soon as possible.
Some say it's better not to add sugar which makes it even less assimilable vitamins. Although this is not proven. Definitely for her drink to a child hesitant better one teaspoon of sugar juice or better add nothing.