We didn't have a steadfast no children rule, but we really only planned on inviting the kids of the wedding party. I had my FI address the invites for his family and friends and I did the invites for my family and friends. He said when he sent the invitation to his friend Joe he addressed it to Joe and Jane Smith (not their real names). When we got their response card, they rsvp'd for themselves and their 3 year old. I told FI this isn't a hill worth dying on. And that by calling Joe and telling him he can't bring his son, when he gets to the wedding he may be seriously miffed when he sees other kids there, and it could potentially be a friendship ending move. FI says he's still inclined to call him.
What do you all think?