The flower girl and ring bearer are generally children that are either related to the couple, or children of close friends. The flower girl and ring bearer should be too young for the roles of junior bridesmaid or groomsmen (younger than 8). Both of these children should go through rehearsal not only with the rest of the wedding party, but also beforehand so that you can make sure they will feel comfortable with walking down the aisle in front of people. In the rehearsal make sure that the child's clothing does not get in the way of their duties. For example, make sure that the petals don't stick to the flower girl's gloves, etc.
For younger children, it usually helps to have a parent sit on the end of one of the front aisles with a favorite toy or piece of candy as a reward. Although, traditionally the ring bearer directly proceeds the flower girl, it is usually easiest with young children to have them walk together. Depending upon the age and comfort level of the children, you can either have them stand with the wedding party during the ceremony, or have them seated with their parents. The duties of the child attendants are as follows:
Attend the rehearsal and rehearsal dinner (with their parents), if invited and appropriate.
Perform role in ceremony
Parents purchase child's outfit