From Vikidia, the encyclopedia for 8 to 13-year-old children that everybody can make better
Whales are marine mammals belonging to the cetacean group. This group includes many fish-like animals such as the baleen whale and the sperm whale. Dolphins and porpoises also belong to this group, though they are not whales.
Whales are not fishes, but mammals: they give live birth to their young and feed them with the mother's milk. The forelimbs of the whales are transformed into flippers, very similar to the fins of fish, which allows them to swim. Whales don't have gills, but lungs: they breathe air, just like us. The only nostril of the whale is positioned above its head, and it is called a blowhole. When a whale reaches the surface after a long dive, it blows air, carbon dioxide, and mucus out of its lungs, projecting many drops of liquid, like a kind of geyser. This has lead to the misunderstanding that whales blow water, or even vapor, through their blowhole.
Whales count among them the greatest animals living on Earth. The greatest of all, the blue whale, can reach up to 30 meters and weigh up to 170 tons, which makes it the largest animal on Earth.