http://www.childhelpusa.org/
Try this site. You can report abuse and neglect through this site.
Lex,
I am so sorry that happened. I am sorry for the child because I know how he felt

, and I am sorry for you because I can see how upset you are over this. You did the right thing by holding him in your arms and reassuring him that things are going to be ok.
Hearing this is very upsetting but I am so glad that you will be handling this.
Big Huggles to you and your nephew!!!!!