She Wants A Kid Free Wedding-OPP

A bride to be doesn't want any kids at her wedding. Her family is outraged by this. On Today's Other People's Problems she needs help settling this argument.

Mike & Kate-
I'm getting married in September and my fiance and I have been working on a guest list and invitations. We are 28 and 30 and this will be a first marriage for both of us.
We both agree that we do not want kids at our wedding. My best friend's daughter and son will be the ring bearer and flower girl and then her in laws are going to pick up the kids so they won't be at the reception.
The problem is my fiances sister. She has 3 kids ages 9, 11 and 13 and is livid that they are not invited to the wedding. I made the mistake of mentioning this to her at Easter when we were discussing wedding details. I thought she and I were friends but now she is on a rampage to get the entire family on her side about how "selfish" I am to have a kid free wedding.
My dad is paying for the wedding and told me I can do whatever I want at my wedding. It's my day. My brother has a brand new baby and is totally fine leaving him with a sitter for the wedding.
I don't want crying kids during the ceremony or kids playing grab ass at the reception. I know I'm not the first bride to not want kids at my wedding. I've been to those weddings. That's where I got the idea.
Now my future sister in law has rallied my fiances cousins and onto her side and it's turned into this big family fight. My future mother in law hates confrontation and is now asking me to just allow kids so that everyone can be happy. What about our happiness on our day? I don't want to start my marriage off on the wrong foot by pissing off my new family but why can't they understand this is my wedding?!
Do you have any advice on how I can handle this situation?

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