Minger did not say what the relationship was between the 9-year-old and the victims, the Peoria Journal Star reported.
Kathryn Murray, Jason Wall, both adults, were killed, as were 2-year-old Rose Alwood, 2-year-old Daemeon Wall and 1-year-old Ariel Wall, the newspaper reported.
Katrina Alwood and her son survived the fire. They did not release the son's age.
Katrina Alwood and Jason Wall were engaged and the parents of the Wall children. Rose Alwood was Katrina Alwood's niece and Murray was Katrina Alwood's grandmother, the Peoria Journal Star reported.
No arrest warrant will be issued before charges are filed because Minger said he's not sure of a minimum age for imprisoning a minor.
If convicted, the 9-year-old faces probation for at least five years but not after the age of 21, Minger said. He also said that the child would likely face therapy, counseling and psychological evaluations. But Minger stressed that time behind bars is not an option, the Journal Star reported.