"What are they eating?"
Translation:Họ đang ăn gì?
Is there any difference at all between "Họ đang ăn cái gì" and "Họ đang ăn gì"?
Isn't the present tense assumed in Vietnamese? Its one of the things that I love about the language.
Not exactly. Vietnamese doesn't have tense and English -ing and Vietnamese đang both mark the continuous, which is an aspect rather than a tense. In Vietnamese, a verb on its own can apply to any time but can be clarified with various markers. I believe that when we get further into the grammar we will find đang used for continuous actions in the past etc too.