Turns out CC isn't as clueless as we thought.
On Saturday, I reminded them that we were going to a birthday party. CC immediately looked worried and said, "Oh, Mama. We're going to the King's birthday. Since I got the Baby Jesus, I need to bring the cake."
I explained that we were going to her friend K's birthday and that her mom would provide the cake.
Ever since then, CC continually checks to see when she is going to need to bring the cake for the King's birthday. The phrase "next year" is just a concept that she doesn't understand yet. Right now, we're on "a lot of days from now" and "I will tell you when."
I am doomed.