Carolyn Hax: Kids weren’t invited to the wedding? Then don’t bring them

My son and his fiancee live in California and will be married there next summer. My entire family has met the fiancee and feel she is warm and friendly. We live in the Midwest and plan to attend the wedding.
My sister has three sons in grade school, and they are excited about this trip, their first to California. Also, my three nephews adore my son and are looking forward to seeing him get married.
However, my son’s fiancee has informed us that only adults are invited to the wedding and she has already informed her family of this. All of her family live in California.
We have asked my son and his fiancee to make an exception, given the distance my family is traveling. So far, we have not heard anything more. The nephews will be attending the ceremony and not the reception, so we cannot understand what the issue is. I think my sister should bring her sons to the wedding and hope for the best. I would appreciate any advice.
For the love of personalized matchbooks, do not, do not, do not bring people to a wedding who have not been expressly included.
I realize church weddings are technically open to the public, assuming this is one, and it’s not uncommon for congregations to have open invitations to ceremonies. (Receptions — closed, of course.) But if you use this technicality to justify defying the couple — as in, not just the bride, don’t think I didn’t catch the implication of “she is warm and friendly” and “sheinformed us” — then you risk souring your relationship with them both, indefinitely.
And over what? The boys’ excitement is heartwarming, yes, but not so sacred that it justifies undermining the very people this event is about.
Your inability to “understand what the issue is” moved my disingenuity needle a second time, too. There are many issues, the most obvious being that other parents on the guest list, the ones who cooperate and leave their kids home with (expensive) babysitters, will be justifiably angry when your three nephews walk in.
The bride and groom will also have standing to hold it against you and your sister for setting them up to look bad in this way. And that would be on top of their deserved outrage that you took matters into your own hands just because you didn’t get the answer you wanted. When you do that, it doesn’t matter what the specific issue is, or how unfairly rigid they’re being; the gall of acting unilaterally trumps it.
Would I have said yes to your request? Possibly. Probably. But it’s no more my call than it is yours.
Something else to consider, to make you and your sister feel better about arranging care for the nephews during the wedding: While weddings can be thrilling for kids, most bring out the bored-and-squirmies. And, there are few worse times to visit a special person than around his wedding. A couple’s attention is usually divided into a thousand different pieces. These kids will travel to California with big hopes and likely receive but one of these pieces at best.

So please take this opportunity to be gracious, understanding, compliant. The cousins can hang out some other, more appropriate time.