Prosecutors in western New York on Wednesday provided disturbing new details about the killing of a 24-year-old transgender man, Sam Nordquist, who they said was sexually assaulted and tortured for several weeks earlier this year in a motel room in Canandaigua, N.Y.

In an 11-count indictment accusing seven people of first-degree murder and a battery of other new charges, prosecutors said two children had been forced to participate in acts of torture that led to Mr. Nordquist’s death. The same seven people had previously been charged with only second-degree murder.

The circumstances of the children’s involvement were not clear from court records, and the children were not identified except by their ages: 7 and 12.

“To have two children have to participate in the beating of another human being, it’s deeply disturbing,” Kelly Wolford, an assistant district attorney in Ontario County, southeast of Rochester, said at a news conference on Wednesday. “It has — I can speak for myself and everyone involved in this investigation — been one of the most troubling parts of this. It’s heartbreaking.”

The killing of Mr. Nordquist, who prosecutors have said traveled from his home in Minnesota to the Finger Lakes region of New York, where he was held captive and tortured, has prompted a national outcry over anti-transgender discrimination and violence. And some advocates for transgender people have demanded to know why the defendants in the case have not been charged with hate crimes.

The new charges announced on Wednesday added first-degree kidnapping, second-degree conspiracy and endangering the welfare of a child counts to each of seven defendants.