Neat idea!
This brings back an embarrassing memory from childhood.
Playing football in the yard, a careless neighborhood kid accidentally knocked two of my baby teeth out.
I remember scouring the grass for them to no avail, then getting in a rage about how I wouldn't get tooth fairy money, so punched the boy, and he started crying and ran home. I don't even remember who it was, but to this day feel bad about that.
When I got home, my parents said it's no problem, just write a letter explaining what happened and the tooth fairy will understand. And that worked.
Being a deviant, I decided to test it a few days later with another letter in secret, to no avail. And that was my first inclination this whole thing wasn't real.