If you are a child needing help you can talk to a trusted adult (like a teacher) who is required by law to report it to law enforcement. You might have been told by the person abusing you not to tell anyone. It is scary to tell someone but it is important to tell someone what has happened to you.
If you are a parent of a child victim, it is also important that the crime be reported and the child be believed. Common to abuse is doubts for the child and loved ones. The justice processes are difficult and painful at best. But protecting and assisting the child has to be the goal.
If you are an adult survivor dealing with the trauma and/or wanting to report a victimization that happened as a child, consider researching support resources as you inventory your options.