In this day and age of blended families, weddings and marriages can be a huge deal when children are involved; and, many of today's brides and grooms have mixed feelings about including their children into the wedding ceremony. Take heart there is no "right" answer for this dilemma. You really have to do what is right for you, your intended and the children.
If you get along with the children and they are mature enough to understand that "Mommy" or "Daddy" isn't being replaced, then including them in the wedding can be a very powerful (and good) bonding experience for all of you. However, if you decide to include the children it has to be all or nothing.
This means if they are to be included in the wedding, then they need to get a say on certain items such as the dress or suit they are going to wear, asking your them to participate in the wedding party, perhaps incorporating a special Daddy and Daughter or Mommy and Son dance at the reception, and, anything else that can make them truly feel included. The worst thing you can do is "force" your will and opinions on the children. No matter how well behaved and how well they listen under normal circumstances, a wedding changes everything, and, the older the children are -- the more they are going to realize what is actually happening, and, it is common to see a rebellious side to come out. Don't fight it, it will only make matters worse. Instead, find out what is really bothering your children.
Premarital counseling can be helpful in some cases, but, if there are serious reasons that your child is rebelling you may want to rethink getting married. At least at that point and time. If you are determined that the time is now regardless of your children's feeling on the matter then that is your right, however, just remember children are children and not robots and cannot be programmed to do ask you wish and ask. Just be prepared for some bumps (maybe even major bumps) along the way.