Shouldn't this sentence should be written without **los**?
Isn't the sentence
Estamos leyendo los periódicos.,
that is written in the reference section in the uses of estar should be written without los?
In this example:
Estamos leyendo los periódicos. (We are reading the newspapers.)
los refers to particular newspapers, not just any. In other situation we could say: Estamos leyendo -- periódicos (We are reading newspapers), Estamos leyendo unos periódicos/Estamos leyendo algunos periódicos (the last two examples would be translated to We are reading some newspapers).