Did a Google thing.
"I hate to disagree with the other posters but really when I have seen Junior Brides they are the daughter of the bride or groom that they don't want to be a flower girl and want more directly incorporated into the ceremony. The parent and stepparent marry and then they have a little joining ceremony to unite the family with the Junior Bride--she gets her own little ring or necklace if they want to make sure she can keep it more than a few years. They are in mini wedding dresses and go from there. I have also seen Junior Bridesmaids be called Junior Brides but that wasn't very common."
You're welcome!