Below you will find my understanding of mandated reporting. Beware: I am not an attorney. But I am a police officer (Chicago) and interpreter who has considerable experience investigating and assisting in investigations of physical, sexual, and financial abuse of people with disabilities.
1) Mandated reporting is not Federal law but state law. However, all 50 states have a mandated reporting law on the books. There may be some differences across states but the requirements are basically the same.
2) The law itself names those persons who are required to report. Usually included are, physicians, psychiatrists, psychologists, mental health workers, nurses, social workers, police officers, teachers, and school employees. Others may be named depending on the state. I have not heard of interpreters being named as a mandated reporter in their own right. The exception would be an interpreter who is an employee of a school. In some states, an interpreter who is an employee of a hospital or mental health facility may be a mandated reporter. Interpreters should read the law in their states and determine if they are included. Usually a school employee will know as they either sign a statement to that effect or receive mandated training on reporting. The law is available in any law library or you can contact your local juvenile court and talk to the prosecutors office. The state dept. of children and family services may also be able to provide you with the law. While I would not expect a private practice interpreter (freelancer - as opposed to an employee) to be considered a school employee for purposes of the law, a prosecutor might so it would be good to ask.
3) If you are required to report, you may not make the report anonymously but you could (in some states like IL) "cause" a report to be made meaning that you go to someone (like a teacher or principal) and they make the report. Also required in addition to reporting is to cooperate in any investigation by turning over notes, files, pictures, or other evidence and testifying if requested to do so.
4) You are required to report a "reasonable suspicion" of abuse. You do not need to have proof and in fact you (or anyone that works with you) should NOT try to prove it or try to obtain proof - that is the investigator's job. You should not decide if there is enough evidence but only decide if you reasonably believe something is going on. If you are not a police officer/detective or prosecutor, you do not know what is or is not evidence most of the time nor do you know what has to be proved (elements of the offense) or how to prove it. Usually when school personnel or other non police people try to "prove" an abuse case they end up contaminating it or otherwise ruining the integrity of the investigation. Worse yet, they either inadvertently tip off or purposely confront the offender so that he a) can get his ducks all in row and b) get to the victim to threaten thereby driving the abuse further underground.
It is also not a group decision. For example: if you are part of an educational team and you bring your concerns to the team and the team decides that there is not enough to report but YOU still have a reasonable belief that abuse occurred, then you are still obligated to report under the law. You do not need to be a "trained" person or make a "diagnosis" of abuse. Whatever you are, if you are a mandated reporter and have reason to believe that there was abuse, you are obligated to report.
5) The RID code of ethics is not binding or relevant to mandated reporter laws as far as police and the courts would be concerned.
6) Mandated reporters are protected from liability for good faith reporting. You cannot be found liable if your report turns out to be unfounded.
7) Failure to comply with the law is a crime. In Illinois it is a class A misdemeanor which can result in a jail sentence of up to one year. Check your own state laws for how it is classified in your area and for what it requires of you.