After having planned my own wedding, I have a strict "rule" that it's not ok to get upset over anything about a wedding that isn't your own. The bride and groom get to do what they want to do and that's that. So if they don't want to have kids at their wedding, they don't have to. No one gets to be irritated about that..
However,
The bride and groom don't get to control other people, nor assume that they understand what their family life is like. They must understand that if they ban children from their wedding, some people *may not come.* This may include close family. It's not appropriate for those without kids (as most getting married couples would be), or anyone really, to assume what is an acceptable situation for someone else's children.
I don't leave my children in strange rooms in the care of people they don't know, as in a a nursery or childcare situation. I don't hire strangers to watch my children (as would be the case at a wedding I need to travel for, where likely everyone I know there already would be at the wedding), and when I have a young nursing baby, I don't leave them. They didn't take bottles and I don't feel like dressing up and then going in a bathroom to pump.
I won't question the decision not to have kids at a wedding, but in return, they don't get to question my decision whether or not to attend.. an invitation is an invitation, not a summons.
Secondly, while I consider not having children at a wedding a valid and individual decision, I do sometimes wonder if this decision represents a desire for control that isn't always realistic. We had no children at our wedding, simply because we got married young and none of our friends or family had any children under the age of 13. But that doesn't mean that nothing at the wedding went "wrong." And looking back, those are some of our most charming moments.
On the flipside, children do also have the potential to create some of the most beautiful moments and memories at a wedding when the bride and groom embrace their presence. My daughter was recently a flower girl at a new years eve wedding for my brother in law that ran until 1 am. There were many other children and babies and I think one of my new sister-in-law's favorite moments at the whole wedding was when she was with my two year old on the dance floor and other little boy came up and uninvited planted a giant kiss on her. There is also a beautiful photo of the bride and groom dancing with my daughters. Now, given, these two plan to have children (and soon!), so it probably really added to their sense of their new marriage bond.
In any case, I think that everyone would enjoy wedding experiences more if they stopped being annoyed at everyone else and did what was right for them. Have kids or don't have kids. Fine. Attend or don't attend. Also fine. That's my take, anyway. :-)
Nicki