As members of a profession dealing directly with children, you have a legal responsibility to notify CAS in accordance with Articles in the attached brochure. You DO NOT have to inform the Principal, Vice Principal or anyone else if you choose to remain anonymous.
It is important for you to understand that if you suspect something, that you are obligated to inform CAS and not ask an administrator if you should or should not. If you choose to let the administrator know that is fine. Should an administrator attempt to admonish you in any way, inform the Federation immediately.
See details here.