Okay kiddo, so there were some really old kings called the Kassite rulers who lived a really long time ago, like over 3,000 years ago! They were in charge of a place called Babylonia, which was in what is now modern-day Iraq. These rulers were called "early" because they came at the beginning of the Kassite period.
Now, the thing with the Kassites is that they were actually not from Babylonia originally. They came from a place called the Zagros Mountains, which was pretty far away. But they managed to conquer Babylonia and become the rulers there. The first Kassite king was Agum-kakrime, who took the throne around 1570 BCE.
These early Kassite rulers were known for a lot of things. One of the most important things they did was build lots of temples and other important buildings. They were also really into art and literature, and they wrote a lot of poems and stories. Some of these writings even survive today!
One thing that's interesting about the Kassites is that they worshipped a lot of different gods and goddesses. They didn't have just one god like some other cultures did. Some of their most important gods were called Shuqamuna and Shumalia, who were the gods of the sky and the earth.
Overall, the early Kassite rulers were pretty important in the history of Babylonia. They ruled for a long time, and they left behind a lot of art and literature that we can still learn from today.