The throat of first-grader Dominick Andujar was slashed when he came to the aid of his 12-year-old sister, the Camden Courier-Post reported Wednesday.
"The 6-year-old saved her life," Camden County Prosecutor Warren Faulk said. "He came to her assistance while she was being assaulted, and as a result of that she was able to get out of the house."
Dominick was pronounced dead at Cooper University Hospital. His sister, whose throat also was cut, underwent emergency surgery.
She identified the attacker as a local man who often played with neighborhood children.
Osvaldo Rivera, 31, of Camden is being held on $5 million bail.
Authorities said Rivera was high on a combination of marijuana and PCP known as "wet" when be broke into the children's home early Sunday while their mother was in the hospital recovering from surgery.
Two other children in the house at the time escaped injury.