To be a flower girl is such a big honor to a little girl. She will feel so privileged and special that you have asked "her" to be in your wedding. This means she gets to live out the fantasy that every little girl has of walking down the aisle in "big girl" heels, a pretty dress, and of course hold some amazing flowers (whether it be petals to throw or a small bouquet to carry).
You want your little flower girl(s) to be coordinated with either your wedding dress or with your bridesmaids' attire. Here are some of favorite little dresses: