A junior groomsmen, typically aged 9 through 12, is an ideal way to include a child in the wedding who falls in between the ring bearer and full groomsman age group. This way the boy can be included in the wedding festivities and ceremonies with tasks and duties specifically assigned to him. While a junior groomsman typically does the majority of the activities and duties as the regular groomsmen, excluding the bachelor party, be sure the duties are manageable by the personality and tendencies of the individual boy. There does not necessarily need to be junior bridesmaids in the wedding party in order to incorporate a junior groomsman.
Have the junior groomsmen escort wedding guests to their seats. Make sure he understands the division of the bride's side and groom's side for guests, if applicable. Teach him to lead ladies, especially elder ladies, by holding their arm and leading them to their seat. Be sure they understand their demeanor and attitude must be composed and match the tone and formality of the wedding.
Junior groomsmen can escort the ladies of the bridal party down the aisle. Pair them with junior bridesmaids if possible. If there are no junior bridesmaids in the wedding party, the groomsmen can escort a bridesmaid for a treasured photo opportunity.
The junior groomsman can also serve as an escort for the flower girl, which will prove to be another sweet photo opportunity. If the junior groomsman is still in a "girls have cooties" mentality, he will not want to escort a girl down the aisle, but can serve as an escort and chaperon for the ring bearer, helping him with the process at the right moment and to behave during the ceremony.
Being at least a few years older that the ring bearer and flower girl of the wedding party could enable the junior groomsmen to supervise and informally babysit the youngsters during the rehearsal dinner, ceremony and reception. Keeping the smaller children entertained is a beneficial way to utilize him and keep the parents and wedding couple from having to tend to the children excessively. Having a play mate for the duration of the wedding events can also help keep the junior groomsman entertained and engaged as well.