We did this with a "dress" that we received from a dear friend in the mail. It was really cute (not Disney-branded, so not related to this thread) and DW and I assumed it was a sundress. DD5 loved it, demanded to wear it the next day, and off she went to Montessori. She received no looks or comments (although I've already mentioned her sense of fasion before, and it was a Montessori so all about free expression), but that night I took a closer look and said "I think this is actually a nightgown". It was so similar in style and material to her sundresses that we didn't even notice. FWIW, it's now worn strictly as a nightgown, but that has no bearing on this thread. I still think if your daughters are fine with it, and you're fine with it, then that is what matters.