Sixteen-year-old John Freeman and 18-year-old Tyler Best appeared in Niagara Falls City Court on Tuesday, about 24 hours after Isabella Tennant's body was found dumped in a trash can.
Freeman is charged with second-degree murder. Police say Best led them to the body. He has been charged with evidence tampering.
A judge entered not-guilty pleas on behalf of both teens. A court clerk says they were sent to jail and ordered back in court Sept. 7.
Police haven't said how Isabella was killed. An autopsy was being done Tuesday.
Isabella had been spending the night at her great-grandmother's Niagara Falls home.
Messages left with Niagara County Attorney Michael Violante weren't returned.