Learning Curve

Conversation between me and Riley while he is practicing spelling on the computer. 

Riley: I wanna spell your name (mom). Me: Okay bud what letter comes first? Riley: M. Me: Good job! What comes next? Riley: O. Me: Very good! Now what? Riley: . . .does that spell mom? Me: No, it spells Mo. Riley: (adds an O) is that mom? Me: No, that is moo Riley: (adds another O) is that M-hundred? Me: No, that's M-thousand.