Damien Bendall, who had been in a relationship with Terri Harris, raped and murdered her 11-year-old daughter Lacey Bennett.
He also murdered Ms Harris, 35, her 13-year-old son John Paul Bennett, and Lacey’s 11-year-old friend Connie Gent.
Their bodies were found at a house in Chandos Crescent, Killamarsh, Derbyshire, on 19 September 2021.
Bendall, 32, admitted the charges at Derby Crown Court, where he is due to be sentenced later.
The court heard Ms Harris was pregnant when she was killed and Bendall raped Lacey as she lay dying from her injuries.
Bendall, of Chandos Crescent, is said to have committed the murders at some point between 17 September and the time the four victims’ bodies were discovered.
