Q&A: Invitations: Noting Number Invited on Response Cards?
Q: Is it considered tacky to write in the number of invited guests on the response card?
A: This tactic will let guests know that only the people to whom the invite is addressed are invited. It's surprising how many guests feel free to bring children or other relatives you didn't expressly invite. But there is a subtler way to do this: Write in the exact names of the people invited (just as you addressed them on the outer or inner envelope), and have them check "will attend" or "will not attend." That way, it will be clear that "Mr. and Mrs. John Smith" or "John, Katherine, and Tommy Smith" are the people invited; all they need to do is note whether or not they're coming.