I know I wouldn't be offended. It's completely up to the people hosting the wedding who they want on the guest list. And these days, it's not just a behavioral issue where hosts are concerned about the potential disruption caused by parents who don't look after their children, but a financial one. Most places charge for children over a certain age and that can add to the expense considerably.
That said, I adore kids. My wedding just wouldn't have been right without my darling nieces and nephews and friends' children being adorable as only children can. And I really appreciated how most of the parents were watching their kids and making sure that they were behaving themselves. However, I could have done without the little boy who decided to use the stage as his personal playground...more specifically, I could have done without his parents and much older siblings who were completely aware of his behavior and did nothing.
It's your child. Take care of him or her. If you want a relaxing evening out, make your own arrangements on your own dime. Don't use social events hosted by others as free babysitting. It's not fair to the hosts and it's not fair to your child who isn't going to learn how to behave properly in social settings.
Oh - and to all the parents out there (and here) who I've seen being vigilant about their young ones...a big fat thank you. It's much appreciated.