Wed2b bridesmaid dress exchanges

Has anyone had any success changing bridesmaid dress sizes due to covid? We had our wedding postponed a few times now and the size 6 dresses I bought the 11yr olds are wayyyy to small now! They are size 8 if not 10’s by now. I was going to email Bride2b to see if they would be flexible on this as clearly the dresses have not been worn and wondered if anyone else had a similar situation?