Wedding guest lists can be an absolute nightmare! At the end of the day, the couple should be able to invite who they really want at their wedding, and that's usually close family, and lots of good friends who they spend time with, not cousins who they have grown apart from.
When my DS & DiL married, they did invite aunts & uncles, but only one or two cousins, who they wanted there. All of my husband's siblings (he has 4) have at least 3-4 adult children themselves (my son's cousins), some with partners, and children of their own. One of my husband's brothers took offence, and declined the invite, because his four adult children, who my son used to spend a lot of time with when they were growing up, but has had very little to do with since childhood, weren't invited! Frankly, my son didn't give two hoots, but it did make for some awkwardness within the family, especially from my MiL!
Many of us have grown up with our cousins, who were probably amongst some of our first friends, but by the time we go to high school, throughout our teens, and beyond, we often go our separate ways, and often have very little to do with them.
I do understand why the OP feels the way she does, as most of us would be a little upset, and feel left out, if we, or our children, weren't included in a family wedding, but I do appreciate and understand why. Weddings are usually ridiculously expensive occasions, and venues have a maximum limit on the number of guests. If my DS & DiL had to invite all of their cousins/partners they would not have been able to invite all of their close friends who they spend time with, and who they have known for many years. Couples don't generally leave people off their wedding guest lists out of spite, it's often down to the cost, and how many guests they are allowed at their chosen venue. So, why should they invite a family member, who they have little to do with, over inviting a good friend who they spend a lot of time with?
If I were the OP, I'd go along to the wedding and enjoy it with the rest of the family. Your children are adults now, and they have still been invited to the evening if they wish to attend.
On that note, I do agree with another poster who mentioned that she dislikes the whole 'day-do/evening-do', and couples have to decide which guests get to spend all day at the wedding. My DS & DiL had a very late afternoon ceremony, followed by dinner, a live instrumental band playing throughout, then speeches, followed by DJ/party until the wee small hours. No separate day-time/night-time invites, and it worked perfectly.