Legal Question in Criminal Law in California

I don't quite understand what you are saying. What do you mean by "let your little sister down?" Disappointing someone is not a crime.

If your little sister has been neglected, physically or sexually abused, or is otherwise the victim of a crime, you should report it to the foster care agency and your local police department.

Individuals do not "press charges." Only the District Attorney can initiate a criminal prosecution. If the police believe a crime has been committed, they will forward their reports to the DA, who will then decide whether to file criminal charges.

You press criminal charges by filing a report with the police. You report child abuse and neglect to Social Services. The parent or guardian can file civil suit for wrongful death, using a local attorney who can advise if there is actual a valid case there.