But, since it did, I decided to look into the derivation of the holiday. Turns out, Grandparents' Day is not a Hallmark creation. It was started in 1956 by a woman in West Virginia who volunteered with older folks and wanted to create a way to honor them. Grandparents' Day became a national holiday in 1978.
What I also learned from googling, though, is that today is Father's Day in Latvia and Macedonia, Day of the Homeland in Germany, and Knabenschiessen (a holiday based around a target-shooting competition) in Switzerland. It's also National Peanut Day.
So we grandparents don't have a lock on this day. Like every other holiday, we have to share it.