Allah sent Prophet Yunus to the city of Nineveh, a great city in Assyria. Its population was around 100,000 people who worshipped idols. Yunus preached firmly, but they refused.
After a long time with no one believing, Yunus grew angry. He left the city without waiting for Allah's command. He boarded a ship and sailed away.
At sea, a great storm came. The ship was sinking. Passengers drew lots to decide who would be thrown overboard to lighten the ship. The lot fell on Yunus. They repeated three times — it still fell on Yunus. Finally he was thrown into the sea.
Allah sent a great fish (nun/whale) that swallowed Yunus whole. In the fish's belly, in three darknesses (the fish's belly, the sea, the night), Yunus prayed:
لَا إِلَٰهَ إِلَّا أَنْتَ سُبْحَانَكَ إِنِّي كُنْتُ مِنَ الظَّالِمِينَ
"There is no god but You. Glory be to You. Indeed, I have been among the wrongdoers."
Allah heard and rescued him. The fish brought Yunus out on the shore. Meanwhile, Allah opened the hearts of Nineveh's people. They all believed — the city that wouldn't hear Yunus now searched for him to learn.
For children: when you're angry and want to run from a problem, remember Yunus. Running solves nothing. Returning to Allah, humbly, is always the way out.