Prosecutors accuse the two men of firing into a South L.A. backyard on Halloween, thinking that rival gang members lived in the home.
Five-year-old Aaron Shannon Jr. was killed after he was shot in the back of the head. Aaron was in the backyard showing off his Spiderman costume to his uncle and grandfather, who were also injured in the shooting
Police say the victims had no gang ties.
Prosecutors said that Denson and Hall could face life in prison if convicted. Both remained jailed without bail.
The Associated Press contributed to this report.