I'm in the minority here, but YANBU in my opinion @ZingyJadePombear I dislike child free weddings and find them snobby, and divisive, and unfair. There are BOUND to be some people who can't go. And it's so mean to exclude extended family like this (And in some cases, friends too.)
If the whole extended family is invited - but no CHILDREN are allowed - someone is going to have to stay and look after the children, so some family members will miss out.
My friend's 2 daughters were invited to her brother's wedding (15 years ago,) as they are his nieces. They were flower girls, (5 and 7 at the time.) But the children of her and her brother's 3 cousins weren't invited (7 children in all, and all under 16.) As the aunts and uncles and grannies etc were going, the cousins couldn't come either.
The relationship was never the same with my friend's brother and their 3 cousins after that. (Or my friend, as her children were invited... so the 3 cousins were pissed off with her too.) They all held a grudge and have never invited my friend or her brother - or any of their (5) combined children to anything. Their DC's big birthday parties, engagement parties, several weddings, nothing.
It's fine to exclude family members children (and the family members themselves) if you don't give a shit about them and don't care about your relationship being affected by snubbing them and their children. You do you. I wouldn't do it. The 'their wedding, their choice' brigade really boil my fucking piss. It's not OK to treat family and friends like this. As my friend's brother has found out (to his cost.)