Chrystelle: It is me to decide

This morning on the way to school, I tried checking if my kids mastered their spelling with the sound "i:".
- Chrystelle, can you spell "thief"?
- Yes I can. It is "t - h - i - e f"
- Very good, I said.
- Claver, can you spell "grief" for daddy?
- Yes Dad. It's "g - r - i - e - f"
- And "leaf"?
- It's "l - e - a - f".
- Great, I said. Back to Chrystelle now.
- This will be the last question, she said.
- Why? It is me to decide whether and when it ends.
- No Dad. It is me to decide for me because it is my mouth.
...
Tell me now where kids get their answers from!