Assuming that's what actually happened, it's not malpractice, it's criminal. If the doctor injected the drug knowing that it would result in a murderous rage, depending on state, it could very well be murder in the first degree. Levels of knowledge and intent would make the actual charge.
In a civil environment (malpractice), the patient's family, the patient, and/or the boyfriend's family, could be entitled to a hefty monetary award. The doctor would certainly lose their license.
If this is something you feel has actually happened, report the details to the detectives investigating the boyfriend's murder.
If the time limit has passed, there is nothing you can do. The only exception is when it's something you didn't know about and then you have a year or so after you discover the malpractice.
It doesn't matter how old the children were, their guardians are the ones who should have filed the suit. Usually it goes based on the age of the victim of malpractice. You can call malpractice attorneys in the state where they incident happened and see if they will take the case. Given how old it is, not very likely.