My sister is dating a guy who just came out of prison, he beats her and takes her money. She has a 5

Yes tell child services before your nephew gets hert.

Don't ask her for a confession, you won't get one. Demand an explanation. I know she is family but if she is even going to still ith the guy. she is going to get everybody in your house in a lot of trouble.explane to her that what she do is wrong.

Report him to the police ask them check
him out + u need papers to file an AVO
Violence Order against him.

I agree with the above also.

Actually I'm not sure if the child hasn't been injured. But the police can for sure if he's beating your sister.

call the cops and have the ass hole arrested

You don't have to exactly call child protective services
As long as you saw him with your own eyes hit your sister then you can report him to the police yourself with out having to get child protective services in the middle, you don't want them to take your nephew the system is bad and always will be &that will only harm ur nephew, afther calling the cops you have to make sure your sister agrees to presses charges and puts a restraining order against him if she doesn't thy most likely will see that she dont care and will call child protective services keep in mine that your making the right choice for your nephews safety good luck.