When the little girls learned how to take their sleepers and PJ's off last winter, my daughter would use safety pins to keep their things on, and ended up having to then pin the sleepers on the inside when they could get the pins off if they were pined on the outside of their sleepers. Now they can dress themselves, so if they get cold, they can put clothes back on.
Her older 2 didn't do things like these two do, it's kind of like 'monkey see, monkey do!' But twins are a lot of fun!