I am in the USA, but I know that laws vary from state to state. In Illinois, Ts are required to report abuse that involves vulnerable populations. That would include children, elderly, people with mental or physical disabilities. If it is verbal abuse, it is a gray area.

Reports can be made anonymously. In Illinois, when there is a report of abuse DCFS (Department of Children and Family Services) does an investigation. This usually involves interviewing the family members. Frequently children will be interviewed at school so that the parent isn't able to influence the child. They would also look at medical records.

Jail time depends on a lot of factors. Type of abuse, severity of abuse, length of time the abuse has been going on. Probation and compulsory counseling are sometimes the result. Or, if DCFS finds there is cause, they can remove the child(ren) even if there is not enough evidence to take the case to trial. In that case, parents are given a list of things they need to do to get their children returned to the home.

Your friend can also call a hotline and report the abuse anonymously. That will trigger an investigation (again, if a vulnerable person is involved). They do not need to tell their T to get things going to protect their family members.