"My nephews are eating soup."
Translation:Mes neveux mangent de la soupe.
In this example, "de la" is called a partitive article. It refers to an undetermined amount of something. "De la" is used with a feminine noun; "du" is used with a masculine noun. "Des" is used with plural nouns.
- Il mange de la soupe = he is eating soup
- Elle boit du lait = she is drinking milk
- Nous mangeons des pommes = we are eating apples
These expressions are never translated as "of the" when used in this way. Sometimes, one could use the English "some" in English, but when the partitive article is used in French, the "some" is almost always omitted in English. It is simply not necessary. Understanding the use of the partitive is a significant step in understanding French. Once you have mastered it (and it is really not that difficult), you will have crossed a hurdle. The reason it can present a problem is that the same words are interpreted differently in other contexts. So we have to understand how to interpret them in context. For a thorough explanation of the use of partitives, take a look here: https://www.thoughtco.com/du-de-la-des-1368977