Mould tends to grow on carton which are open for long enough, so that’s something worth looking out for. But it’s not only that, that can be harmful. Because of the specific opening, air can get inside and cause the fermentation of sugar and causing the juice to turn into alcohol.
Although it is not considered as dangerous it can cause an upset stomach, that is why one should avoid situations in which you drink from a carton with mould on it or a carton which has been open for long.
Sweetened juice can also cause obesity and drinking too much pasteurized juice can cause diarrhea, tooth decay and flatulence.
According to research conducted by the Americano Academy of Pediatrics, it is not recommended to serve juice to children younger than 6 years, unless it is home-made. Even then, the amounts should not be big. Although juices are considered as healthier than sodas, they should still be given to children with caution.