Okay kiddo, so Nestorianism is a big word that has to do with how people in the past understood Jesus. You see, some people believed that Jesus was both fully God and fully human, like a superhero. But other people, called Nestorians, thought that Jesus was really two different people - one was God and the other was just a regular human being.
It's kind of like if you have a toy car and you pretend that it's really two different cars - one is the driver and the other is the car itself. But other people might say that's silly, because it's really just one car with one driver, even though they're different parts of the same toy.
The Nestorians believed that Jesus had two separate parts - the human part (which was like the driver of the toy car) and the divine part (which was like the car itself). This was different from what most people believed, and some thought it wasn't right or true.
But even though people disagreed about Nestorianism, it's still important to learn about and understand different beliefs and ideas. It helps us to be open-minded and respectful of others, even if we don't always agree with them.