Court records say Nashika Bramble and Madani Ceus have been charged with two counts each of first-degree murder on top of previous charges of fatal child abuse.
Attorneys for Bramble and Ceus couldn’t be immediately reached Tuesday.
Police have said the girls were between the ages of 5 and 10. Their bodies were found in mid-September on a farm outside Norwood, about 30 miles (48.2 kilometers) west of the ski resort town of Telluride.
Three other people also face fatal child abuse charges in the girls’ deaths.
It’s not clear how any of defendants were connected to the children. Authorities haven’t released any details about what caused their deaths.