Me and 小tz: "Curly curly 豆豆, Curly curly 豆豆, change!"
小tz: "Daddy, I change you into a frog."
Me: "I change you into a fly! Hehe... now I can eat you. La, la, la~ "
小tz: "Daddy, I say FORK, not FROG. Na, na na bu bu."
Me: "... ... ..."
By the way, 小tz taught me that while saying the phrase, you need to draw circles using your index finger then point at the person you want to change.