Winged Sandals from Australian Broadcasting is a wonderful site for kids—probably the best. It includes an great How Apollo got his oracle and an amusing Ask the oracle. I asked if anyone was wiser than Socrates, but it responded:
"You have the potential to be great; but nobody can be great without the help of the gods."
History for Kids: Oracles. The copy is so-so, but the ads are terrible.
The Oracle of Delphi: True, False or Both? by Alexander Easton Traub. Grade-school paper, one of a number in the project Greek Mythology: The Facts That Made The Fiction. The paper is fine as far as this sort of thing goes (although I'm not sure how I feel about "With the rise of Christianity, the temple started to lose its excitement"). I cite it here to note the spread of an intellectual tendency to "explain" ancient myth in historical or scientific terms. (Other papers rationalized the Argonauts, the Trojan War, etc.) Although quite dead in the scholarly world, this sort of explanation has powerful popular appeal, and continues to be taught to school kids. In the end this is a limiting way to think about Greek myth, casting it in simple, familiar and final terms instead of prompting an attempt to grapple with the complex and exceedingly alien culture which gave it birth and continued to invest it with significance.
Lesson Plan: Twentieth-Century Oracles by Anthony F. Franco (for English classes, 8-12 grade). The author moves from a brief discussion of Greek oracles, especially the oracle of Delphi, to locate modern oracles in various modern social institutions which have similar functions.
"The unit attempts to draw parallels for modern students between the ancient Greek tradition of oracular consultation and five groupings of modern day oracles which can and do influence their decision making process.Includes a good starter bibliography for students of all ages.