The Prophecy of the Twice-Blessed Child

The term of Twice-Blessed Child is first used in Season 5, The Day The Magic Died.

It refers to the prophecy of a special child holding great magical power and wisdom; with proper nurturing, the child will grow into a powerful force, whether good or evil.

Wyatt Halliwell: the offspring of Piper Halliwell and Leo Wyatt, is the child.