The flower girl is as important as your bridesmaid in a sense that she will walk down the aisle with you. In fact, the age of a flower girl is usually between 4 to 8 years old and choosing a dress for her will be a bit different from the way you choose your wedding dress.
Sometimes the dress of the flower girl is a mini version of your wedding dress. However, the body frame of a small girl is a lot different from an adult female, a mini version of the wedding dress can look very funny since the proportions of the dress is twisted. As a result, you may consider a dress which is not just a copy (with a smaller size) of yours.
Traditionally the dress of the flower girl should give the little girl a bridal look. It is in fact very good since in this way the girl can be tied to your wedding. The dress of the flower girl is usually white in color, as in the case of your wedding dress. A beautiful dress can make your flower girl look like a princess. However, you cannot just consider the aesthetic aspects when you are choosing the dress for your flower girl.
As in the case of choosing a regular dress, the number one issue you have to consider is comfort. You flower girl should feel comfortable when she put on the dress. You have to bear in mind that a little girl is not like us adults. There may be misbehavior if they do not feel comfortable. To this end you have to really make sure that she feels comfortable when she is wearing the dress.
Even if you are not thinking of the problem of misbehavior, there is still no point to make your flower girl feel uncomfortable. At the end of the day she is one of the people who help you in your wedding, although she is only a little girl.
Besides, you should discuss with the parents of your flower girl when you are selecting the dress. This is especially true if the parents are going to pay for the dress. You choose a flower girl because she has some special connections with you and there should also be some special connections between you and her parents. You do not want her parents to pay for something that they feel unaffordable.
If the parents of the girl really find the dress a bit unaffordable, you should try to arrange to see if you would pay for the dress. You may need to select another dress which is more affordable in this case.
Another thing that you have to consider is the size of the dress. You may order the dress for your flower girl a few months before your wedding. However, little children grow very fast. They may become taller after a few months and the dress will not fit your flower girl well. In this case, you can order a dress with longer sleeves for example, and have it change a week or two before your wedding so that the dress can fit your flower girl well.