Untold years ago there was an end of things. Nukes rained down on the earth and the world was destroyed. The combined nuclear fire set off uranium deposits in the Earth and afterwards, only the wasteland remained. Many chemical and biological weapons were released. Only the very strongest people survived and carried on.
Humans kept reproducing, having babies, raising babies in the safety of the underground vaults. Most were not so lucky. There were babies in caves, babies in the wastes, babies near trash, babies suckling the nutrients out of mothers who could barely survive themselves. But over thousands of years, the wasteland changed.
No longer can you find a can of beans, or evaporated milk, or packaged jerky and twinkies, just empty packages where someone else has gotten there before you. Humanity learned to hunt the mutated creatures of the wastes to survive.
For uncounted generations wastelanders have feared the giant scorpion. They say the scorpion was once a the size of a cat but over many generations it grew larger as the smaller, more stupid ones were killed off. Soon the tables were turned and we became the hunted.
No one ventures out at night when they are out to feed. It is certain death. Unless you are lucky enough to have a rocket launcher, let alone a supply of rockets. Most wastelanders carry a spear, and if you’ve traveled the wastes long enough they called you a tribal.
Things are evolving. The wasteland is changing. Mutant fruit trees grow in the cracked earth. Iguanas wander the wastes, consuming what insects remain, and they are hunted for their succulent meat.
Eat enough of anything and you'll die of radiation. Everyone dies of radiation. You don’t see any old folks, just young, fearful faces, and you learned to eat less or perish even earlier, and if you’re really unlucky, you'll go feral, lose your humanity and become an animal.
To live is to die. That's the first thing every kid learns in this god forsaken hell.