*A wedding is usually one day, it's meant to be the couple's day l, so let them choose what they want.
I think you are being unfair, majorly, in deciding a couple are a certain way because they choose not to have children at their wedding.
Lots of couples, I am sure, enjoy having a night out without their children. It doesn't make them bad people.
You are totally generalising. You don't know the op's friends.*
This isn't a night out, it's a wedding. Of course people don't want kids on a night out, that's completely different.
Yes its their one, special day (if they don't divorce or aren't already divorced) and I think its significant that they choose to make it a "child free" one.
I know they've made their wedding 'no kids', even though at least one close friend has them. And very likely other family members and friends.