Okay kiddo, so imagine there is a big group called the government who make decisions about how the country should be run. There is also another big group called the opposition who do not agree with the government's decisions and want to do things differently. The official opposition is the main group of people in the opposition and they have a special job to do.
The official opposition has a group of people called the shadow cabinet. They are called "shadow" because they are like a copy of the actual cabinet that the government has. The shadow cabinet has important roles too - they each "shadow" or follow around one of the people in the government's cabinet. For example, if there is a person in the government called the Education Secretary, there is a person in the shadow cabinet who follows them around and is also called the Education Secretary.
The job of the shadow cabinet is to watch everything the government is doing and figure out if they are doing a good job or not. If the government is doing something wrong, the shadow cabinet can tell them and suggest different ideas that might work better. They also try to get other people to listen to their ideas and agree with them, so that they can hopefully become the government one day and make the changes they want.
Overall, the shadow cabinet is like a group of superheroes who want to help make the country better, just in a different way than the government does.