Piper tells Phoebe that unborn babies don't perform magic in the first trimester. Throughout season 5, Wyatt performs magic from the womb (including the first trimester.)
The Seer's entry in The Book of Shadows reads, "An upper-level demon who has been around for thousands of years. Because she has the power to see the future, she is a top adviser to the Source of all evil. In fact, she has serve multiple Sources, choosing to remain close to the ultimate power. She is a magical craftsmen and master of spells and tonics, but only kills when she has to."
The Tall Man's entry in The Book of Shadow reads, "Oral tradition tells of a giant whose body served as a portal to other dimensions. Because he was imprisoned centuries ago, nobody knows what this demon's name is or if he even exists. There's no known vanquish for him. The Source was so threatened, he condemned the giant to spend eternity in a cage."