Convincing a Preschooler

Greyson: When I wake up from my nap, you can play dominoes with me just twice ok?
Mama: Twice? Hey Greyson, do you know what three times is? Thrice.
Greyson: (laughing) You know what four times is? Fice!
Mama: Seriously Greyson, it's a real word.
Greyson: No Mama, you're silly.