As if kids weren't part of (or perhaps even the POINT of) the family.
No, children are NOT the point of the family. A man and a woman joined in marriage are a family whether they have children or not. I know this isn't going to be popular on a parenting website but it's true - children aren't fashion accessories or optional extras but they are NOT the point of a family. A family can be a family without children.

TBH, I don't attend no-child weddings. If DS isn't welcome somewhere then my entire family isn't welcome. I remember being left out of a wedding age 7: "why am I not invited - am I bad? am I naughty? do they not love me?" Yes, at seven you're a bit too into yourself. Same with anything. If one member of my family isn't welcome, none of us are. But then, if I'm not welcome DH and DS don't want to go either! Similarly, I wouldn't go anywhere that banned DH.

I wouldn't mind DS leaving early if only someone would take him early! We've ducked out early of three weddings this year because DS was tired. But if he's not welcome then neither am I.

As for the age cut-off or exceptions - that's up to the bride and groom. There are many reasons to ban children, such as none in the family (I didn't have children there simply because none of my guests to the main bits did) or cost of food etc: it shouldn't be seen as a personal slight. Nor should exceptions. But if you feel strongly about it, don't go to the wedding.