Alright, kiddo, let me explain to you what the Bølling-Allerød warming is all about.
Imagine that the Earth is covered in a big, fluffy blanket that keeps it warm. This fluffy blanket is made up of gases like carbon dioxide and methane, which trap the heat from the sun and keep it from escaping back into space. This is called the "greenhouse effect."
Now, sometimes the Earth's blanket gets thicker or thinner, depending on how much carbon dioxide and methane are in the air. When it gets thicker, the Earth gets warmer; when it gets thinner, the Earth gets cooler.
The Bølling-Allerød warming was a time period that happened about 14,000 years ago, when the Earth's blanket got a little thinner and the Earth got warmer. This warming was caused by a lot of things, like changes in ocean currents and the way the Earth's (wobbly) orbit was tilted. But one of the big reasons was probably because of all the huge amounts of carbon dioxide and other greenhouse gases that were released into the air.
During this time, the world got about 4-6 degrees Celsius warmer than it is today. That might not sound like much, but it was a BIG deal for the plants and animals living on the Earth. Some species of animals had to move to different parts of the world to find cooler temperatures, and some plants had to adapt to survive in the new, warmer climate.
So, that's the Bølling-Allerød warming in a nutshell. Basically, it was a time when the Earth got a little warmer and everything had to change to keep up. But don't worry, kiddo - the Earth's blanket is still here, and we're still trying to figure out how to keep it working the way it's supposed to.