What were the major reasons that led to the fall of the western roman empire, but in a way that a 5 year old could understand

Hey guys, I'm trying to write a children's book about ancient Rome, and I am trying to write a simplified, easy to understand story of the fall of the western roman empire that a 5 year old could comprehend. I am trying to make it focus on the topic of unity and what happens when people are too divided to work together. I know that there was a lot that went into this topic, but I am trying to simplify it so a small child could understand, what are the main events that I could simplify in a way that a small child could understand it all.