Getting married can be stressful, but getting married while also being a parent can add even more stress. No matter what their age, finding ways to include children in the wedding can go a long way toward making sure that everyone is comfortable in the new family.
Older children might participate as bridesmaids, groomsmen, or readers. Younger children may appreciate something like the Family Medallion service that reasserts that the new marriage is forming a family. Roles like junior bridesmaid, ring bearer, and flower child are usually meant for cousins, nieces, nephews, and the children of friends. Not for children as intimately involved in the wedding as those of the bride and groom.
Whatever you decide to do, make sure to discuss it with your children first, and get their input.