Personally I wouldn't have an issue being asked not to take my child no matter what age if there known and trusted babysitters on hand e.g grandparents/aunt/uncle.

But travelling interstate or overseas it is different. There is no way I would trust someone else to find a babysitter for my kids, so asking someone to travel that far and not include the kids is a bit rough. If it is a case of not being allowed due to venue, then I am sure people would be respectful of this, but I would want to know that is the reason, and I am sure the bride/groom would also respect my decision not to go.

But also as someone else already mentioned, it is possible the bride isn't aware of the full needs of a child if she doesn't have any. I know my perspective changed when I couldn't give the baby back ..