If only we were in your situation!!
We originally had no problems with people bringing kids as our flower girls are OH's 2 nieces and my nephew is our pageboy. Only then did we work out that if everyone we knew bought their children along we would have 26!!!
I am not against kids at all but at our engagement party the other week, there were 15 children and although MOST of them are well behaved usually, they bought out the worst in each other and ran riot! Add another 11 to that and I think we could have some problems on our hands!
Also, we have a huge lake at our venue so that poses a health and safety issue for the parents to deal with.
At our engagement party all parents had left by 9:30..... with parents to 26 children, we would have a lot of early leavers at our wedding!
Sorry for crashing your thread with my own children issues!
Think it is terrible that they didnt tell you they were not bringing children as thei names was on the invite. If she couldnt bring her husband with her for whatever reason, I doubt she would keep that quiet?! Funny how people are about children.... like you say, if they are invited they want to leave them at home, if you dont invite them then it is the worse thing ever!!