I'm close with one of my best friend's family. I invited them to my wedding, and FI and I had decided no children. Well, that didn't seem to be an issue. A few weeks ago, I saw sister and she said "I sent my response, it says three because we're bringing the baby". Friend said that she spoke to her sister about it. I hadn't said anything at that point because I was floored since she knew. A friend of mine isn't able to travel because she has no one to watch her baby. I wasn't about to make exceptions for one and not the other.
I thought the situation had been dropped. Now, 9 days out, I found out that she still intends to bring the baby. There are people coming who found sitters and now I'm about to look like an idiot to them. How do I address this without coming off as nasty? She had someone to watch the baby, then decided she felt more comfortable bringing her.
ETA: I even offered to hire a sitter to be there that night to make it a little easier.