When I started teaching Japanese in the US, I started from Hiragana-game. Karuta is good one! Because each card has a picture and Hiragana, so student(s) can learn visually. Youngs loves to have fun to learn other language. Also, teaching a simple Japanese song is another fun thing. If you find out something wrong or students doesn't like what you do, you just change different way. Please don't afraid to make mistakes and how student(s) react on your teaching. If you can ask the girl's mother about what does she like to do, it may be a hint to find the way to teach.