We're having an almost child free wedding (2 under 2s are invited).
No more than that purely because of costs. Weddings are expensive and I'd rather see my whole friendship group than half of them with their kids (who I rarely see). Our venue said for kids over 6 we paid for adult meals.
I know it makes life difficult for parents and we understand that some people can't come as a result, but more people can come than if we had invited children so works for us.