Well, if these things are happening in a church, then the church is allowing them to happen. I guess if the church doesn't think it is disrespectful, then who am I to judge?
Goldilocks--it isn't that I disagree with you. I've been to at least one wedding where the theme overtook everything, and I do think that bridesmaids in costumes is a bit over the top in church.
Theme the pre-wedding activities, theme the reception, but tone it down a bit for the wedding if it is in a church. If you are getting married in a secular venue, then do whatever you want.
Flip-flops? Well, if you can't see them, or they go with the dress, I'd internally roll my eyes but say nothing. And wonder if, 20 years later, how the bride would feel about the flip-flops in her wedding pictures. But not the hugest issue. And I know one bride who had to wear sneakers because of foot surgery a month before the wedding. She bedazzled them.
As for kids in weddings, for really young children, I think you have to be prepared for them to freak out moments before the walk down the aisle starts, and be prepared to pull them out of the procession. That's what's happened in various weddings I've attended--you see a parent sneaking down the side aisle with a small, dressed-up moppet in their arms as the bride starts down the aisle.
But again, if the church allows Star Wars costumes, then I guess you have to let them pass. Most of the weddings I attend are in Catholic churches, and there has been a clear movement in recent years to eliminate secular music during the wedding ceremony. Decorating has always pretty much been limited to floral arrangements on the altar and the pew ends. Since the altar arrangements are left there for the weekend's Masses, they have to be appropriate for a church service. At most Catholic churches, the couple has to meet with someone (either a priest or someone in charge of weddings and other sacraments) and I'm pretty sure that guidelines about what is and isn't allowed are set out plainly during the meetings.
You have the reception to dress in fun outfits and carry out any themes that you'd like. When two professional skiers got married, they had the reception at a restaurant on the slopes of a ski resort--we all had to take the ski lift up there. The bride and groom on the wedding cake were skiing figurines with a little veil added to the woman's head, and the cake was shaped like a mountain, that sort of thing. But the wedding itself was in a church and properly respectful.