Don't they learn early?

My sister was thinking about bringing her son along with us to take the kids to the zoo tomorrow. I told my oldest daughter that her cousin might be joining us and she said "I'm mad at him, though" (Apparently, they got into a bit of a quarrel last time they played together.) I said "Well we already invited him so you'll just have to stop being mad." She thought a minute and said "Call him and tell him we got sick."