Well... at least an improvement?

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.