This is not a children's tale, though (despite inspiring part of the Pinocchio story). It is a vivid testimony of the power of God -- Jonah runs from God, but God catches Jonah; Jonah is cast into the sea, but God saves Jonah in a fish; God sends Jonah to a foreign city (Ninevah, the capital of the Assyrian empire) with a warning of destruction, which Jonah half-heartedly repeats, but the people of Ninevah respond dramatically to appease God; Jonah is frustrated by God not killing all the people in Ninevah, and God tries to teach Jonah a lesson with a sheltering bushy plant.
Arguably, this is an allegory -- a story that means to teach a broader lesson through a few characters. This is not because of the fantastic elements of the story -- a swallowing fish, a city that completely repents its sins virtually on a dime (and makes all of the animals atone in the same way the humans atone) -- but because it seems to highlight the short-sightedness of the Jewish people.
Often, with the benefit of hindsight, we wonder how this people, given so many opportunities and blessings by God, could have stopped following God. Here is a story about this -- while the Hebrew Jonah is God's prophet, it is everyone else who seems more faithful. Jonah is reluctant about his mission for God, but foreigners respond powerfully to God, especially the king of Ninevah, who orders everyone to fast, wear sackcloth, and pray to save the city. In some ways, Jonah seems to point out this Jewish "half-heartedness" in following God's teaching. Or it is simply the story of God using a person for good (the salvation of a large city) despite the fact that the person only seems to care about what happens to himself.