CHILD BEING ABUSED...WHAT SHOULD I DO??? HELP!

My 12 year old nephew... a smart, happy, adorable child. Comes from a family whos parents are millionaires, lives in a mansion, gets good grades.. Seems like he would have the perfect life..

...... but unfortunately, he has been abused ever since i can remember. Being his aunt i cant just ignore it.. but theres nothing i can do. when i speak up to my sister and say that what is happening is wrong... theres always a fight, which results in my sister telling me that it is none of my business.
But how can it NOT be my business? My nephew and i being only 6 years apart..He's like my little brother! He has no one to go to. Both his parents do this to him, and he cant talk about it to anyone else, althought we all know it happens. and no one stops it! i cant take this anymore. i cant see my nephew be treated like this. what can i do? just sitting here thinking about what he goes through makes me sick to my stomach. i want to go over there and rescue him. my father abused my sister while she was growing up.. so does that make her think that abusing her son is okay??? its NOT. and i cant take it......... his father punches him, his mother hits him in the head. they treat him.. like... hes nothing. and his little sister is only 6 but shes catching on to what happens. she draws pictures of it, and writes stories about her brother getting hit. And when she lets it slip she immediatly catches herself and says "oops! im not supposed to tell anyone!". this isnt right. Im not an abuse victim myself, but everytime i see my nephew get hurt, i feel his pain. I hurt for him. I sit and cry about what happens to him. for hours.

I dont know what to do. Is there anything i can do? Someone pleaseeeee help.
<3

you can talk w/ an adult you trust....be it your parents or someone at school.....you can make an anoynmous call to children's services or abuse hotlines....doesn't have to be anoynmous either.....just tell them what you have seen and know about and they will start an investigation......

Ya.. talking to someone at school? i dont think my professors in college will really care... lol. is there any way i can approach my sister about it? i thought maybe sending an anonymous letter in the mail to her... i dont know... grrrrrr