When I sent out my save the date cards,I put our wedding website on the cards so people could see the progress we were making with the wedding. On the website, I put "A Special Message: Because of the limited space at Whispering Pines and our big extended families, we will only be inviting adults and children over the age of 12. Sorry!!". This gave everyone 9 months of notice that there children would not be invite if they were under 12. I also made all the children in our immediate family part of the wedding so people couldn't play the "well she/he is here" game.