SoCal etiquette dilemma. 18+ over wedding or not?

FH and I don't want kids at the wedding. Our venue has a "party" kind of vibe and we just don't want to deal with crazy cousins/children. We are debating on making it 18 and over. However, we have a problem.

Problem #1: My mom wants one of my cousins (I'll call her V) invited. V is the youngest of her family. Her parents and all of her siblings are invited but she won't make the age cut.

Problem #2: FH has family who would potentially be flying in from another state. We would feel terrible if the kids of that family, only 2 kids, couldn't come. It doesn't make sense to have the parents fly out and the kids can't.

Possible solution we thought of? Make the wedding 18 and over BUT have V and the other 2 kids be flower girl/ring bearer. We thought maybe they would be excluded from the age restriction. Any guidance or ideas to bounce off of would be appreciated!