@hl Mr (now) 9 lost a tooth that fell out, so I got him to write a letter to the tooth fairy, and have a nice memento as a result.
Six days later he finds the tooth, and conspiratorially tells me he's going to put it out for the tooth fairy, as they won't know it was the lost tooth.
There's no winning in this situation, so the tooth fairy stumped up cash both times.