Original: The tradition is still very much alive and well in Ireland and Great Britain, where it is common for young children to believe in the Tooth Fairy. When a child's sixth tooth falls out, it is customary for the tooth fairy to slip a gift or money under the child's pillow, but to leave the tooth as a reward for the child growing strong.
Simplified: The Tooth Fairy will take the tooth away while the child is sleeping and leave some money in its place.