If I say "The boy and girl are..."
I think it's as correct as "The boy and the girl", as some natives told me that.
Do you confirm?
But what is the rule in English for non repeating the article?
And also, more generally, are there other rules for omitting the singular article? When could it be implied? (I don't mean the zero article, like in generalities, categories and plural, when we expect the zero article.)