I think there are 2 kids not coming and 1 that is in it. An invitation was extended to Nanny and the sister but that doesn't mean they have to come. One of them could watch the children. Perhaps they could go have a fun time with Dad, paint pumpkins, go to the science museum...
I do not care for children at weddings. They DO tend to have a ball at the reception -- too much of a ball. They're running all over the place, all over the dance floor, rubbing their fingers on the cake or otherwise trying to be the center of attention. Their parents aren't watching them or if they are, they aren't enjoying the wedding. It's a free-for-all. After seeing kids at my sister's wedding, I opted not to have any at mine. It was VERY expensive per head and just like you would take your kids to Red Lobster but not that exclusive reservations only romantic french joint with you and your boo for Valentine's Day... everything isn't appropriate for children. A wedding is the bride's ULTIMATE VDAY. They do not understand the seriousness of what is taking place or the planning, effort, and expense involved in the occasion. They're just out showing their little arses. Plus, I don't like children anywhere there is free-flowing liquor. It's not appropriate.