I've been a major lurker. I figured it was only a matter of time before I needed your help. 
My fiance and I have decided we don't want kids at our wedding. Our venue only allows 125 people, children take up seats, and my FH has a huge huge family. I have a bridesmaid who I am good friends with. She lives about 5 hours away from where our wedding will be. I just found out she's pregnant, and will have the baby in January. I'm really happy for her, and this is really douchey of me, but I did think about what that meant for our "childless" wedding. I had spoken to my friends with kids that would be attending, and all was well. Obviously my response to her being pregnant couldn't be "ohh by the way, you can't bring your baby."
She will be breast feeding, I'm sure. I can't not allow her to bring her baby. My problem is that she is married to a man who had a son before they were married. How do I allow the baby to come - but not her 5/6 year old stepson? I just can't give up a seat to a kid when we're not even allowing our neices and nephews.
I'm having a really hard time with this. I want her there, but I also specifically didn't want babies crying at the ceremony..
So, really, what are my options here?