It depends on what you change in the base sentence. According to linguistic theory, "Your son goes to the place" could be changed to either "Your son goes to where" or "Your son goes where." The order is then changed to put the question word at the front of the sentence, and a form of DO is added to the sentence. Ending a sentence in a preposition is fine.
I suspect that this particular case is an exception since the construction "going to…" suggests that another action will be taken in the future. Since both "Where is your son is going to eat?" and "Where is your son going?" are fine, "Where is your son going to?" sounds confusing. The verb go makes the preposition feel out of place.
Contrast with give. "Your son gives the card to you." goes to "Your son gives the card to whom?" which resolves as "Whom does your son give the card to?" Since whom is no longer in common usage, "Who does your son give the card to?" would also be fine.
I'm from Canada. I guess this could be a difference between a prescriptive and a descriptive style, particularly given that language evolves constantly in many different places. When studying English, I was taught the prescriptive language which I think is what you mean when you say "correct and proper English." As a linguistics student I'm more interested in how the language is actually used, and acknowledge that what is considered "proper" changes over time. For references, all I can say is that my statements reflect English as it's used by people I know. I recognize that it may well be very different in other places. It might be more accurate to say that the acceptability of ending a sentence with a preposition depends on what style of writing you are doing, but that it won't even be noticed in casual conversation among native English speakers here.
In the Spanish the simple present is also for the present progressive and the near future. h. In Spanish the present progressive is strictly for actions going on in the moment you are speaking not habitual present actions or the future like in English. If you said a native, Estoy trabajando, he would expect you to be working right now.