"Generally who visits their parents more, sons or daughters?"
Translation:Generalmente chi visita di più i propri genitori, i figli o le figlie?
I'd' say that when the subject is not clear, Italian tend to use the singular form.
Incidentally, the use of the plural in this very specific sentence, would change the meaning completely: "Chi visitano di più i genitori, i figli o le figlie?" = "Who do the parents visit more, the sons or the daughters?"