You can tell them “NO, do NOT play with the curtains!”, “Be careful guys, please do NOT pull the curtains!” and a whole list of concoctions involving the words NO and DO NOT, but they will still go back.
You can put them on the naughty stool over and over again, but they would still be giggling away and playing with each other in and out of the curtains. Their laughter and squeals have even led me to believe that they are genuinely enjoying themselves!
You think it’s a kid thing?