Wedding Invitation

I'm so frustrated!

I just need to vent... A few weeks ago C and I decided to FINALLY send out our OOT guest invites. Due to the sheer size of our guest list we decided to have our reception without children. Many of the family members both on my side and C's side have children and we'd have 25% more people if we included them. Our ceremony will still be open to all so we figured it wouldn't be a problem. We even decided we'd arrange child care if necessary, as I mentored a lot and have a lot of teenage girls who'd be willing to do this. We addressed all the invites to my family and friends (they are the only ones from out of province) and called our parents to let them know of our decision. Right away I knew C's mom wouldn't love the idea because her side is very close, however she seemed to accept it.
Then, early this week she called C to tell him that while she was at her sister's place the night before, her six year old neice (whom I adore) excitedly showed her the dress she had purchased for the wedding. C doesn't want to ruffle any feathers with this whole thing, and told his mom that we'd just have to let the kids on her side come. I'm so upset. I've tried to be patient. Since our engagement she has treated me differently and been very critical of all the decisions made about the wedding. She is unhappy with our chioce of decor and menu and has made no secret of it. On top of it all, we are hosting the wedding ourselves but she wants to invite 30 of her own friends, all of which C doesn't even know! We offered to let her invite her friends as long as she cuts it down a bit. With this, she stated if she couldn't invite them all, she wouldn't invite any. I know we have to let the children thing slide now. It's too late to change this, but I'm starting to feel like this is family reunion on C's side and a party for C's mom and I'm just a guest in a pretty dress. It's probably selfish of me, and I know that I too have contributed to the problem with C's mom due to my recent hostility towards her, but really. How much did she expect me to take? I know I'm putting C in the middle, but I do feel like he needs to back me up. Especially because we made this decision together! What would you do in this situation? Is there a way for me to get my point across now, without adding to the tension with his mom?