Holy Cuteness! Love little Luma in her jammie jams! Adorable!!! Tell her that KS tends to steal her Mommy's credit card too and order things she shouldn't.....
I have used hot glue on fabric things for scrapbooking before and it seemed to hold pretty darn well. They have adhesive backed Velcro, but I am not a fan of it. I made the mistake of using it when I first started sewing and it would pull on KS's hair! Took it right off. Someone mentioned they have iron on Velcro I think? That would be an easy fix. Worst case scenario, take the dresses to the dry cleaners or tailors. They could fix it up for you in a jiffy!
I know some of these sewing pro's will be of more help than I though.