2. Invitation confusion.
There is nothing more frustrating than when a guest assumes they're receiving a plus-one you had no intention of inviting (we meet again, random bar hookup #22). This can happen even if you address the wedding invitations using proper etiquette.
How to deal: Don't dodge the question—it will only make things more awkward. I'd recommend addressing the miscommunication kindly. Please don't tell someone who thought their children could come that you "can't have them there because weddings with kids are tacky" (true story). Avoid confusion by writing the names of the guests you want to invite on the response card and having them check off a "will attend" or "will not attend" box.
Photo Credit: Pearl Beach Paperie