"Who do the children learn from?"
Translation:ממי לומדים הילדים?
The children are the subjects of the sentence, the ones doing the learning. Et is a marker for objects.
Basic recap: הוא אוכל את התפוח he eats the apple. The apple is the object as it is having something done to it.
I can see that there are two answers and the order of the verb and the noun doesn't matter. Is this generally true? What is the wider grammatical rule related to this? can i say רצים הילדם instead of הילדים רצים ?
You can't really say ?רצים הילדים. It would be understand but it's non-standard. I guess the reason this sentence can be either ממי לומדים הילדים or ממי הילדים לומדים is the preposition at the beginning: ממי.
Does ממי לומדים הילדים sound more natural than ממי הילדים לומדים? Or are both sentences fine?
The first one is the proper and better form when writing, and the second is more common in everyday speech, or in informal writing.
Generally, when the subject-verb part of the sentence is first, it is non-standard to switch them. But if anything comes before them - a question word, a time description, a place description - they can be switched.