Okay, kiddo, let me explain what miscarriage of justice means. Sometimes, grown-ups who work in the justice system, like judges, lawyers, and police officers can make mistakes. When this happens, an innocent person might get punished for something they didn't do, or a guilty person might not get punished at all. This is called a miscarriage of justice. It's like playing a game of tag, and the person who is "it" accidentally tags the wrong person, and they end up losing even though they didn't do anything wrong.
It can happen because people might not have enough evidence to prove what really happened, or they might not have all the facts. Sometimes, people might not even realize they made a mistake. When this happens, it can be really unfair and cause a lot of problems, especially for the person who was wrongly accused. We want to make sure that everyone gets a fair chance, and that's why it's really important for everyone to do their best and make sure they get everything right.