The treatment plan typically takes 15-18 months to complete but can be finished in 12 months, attorney Cesar Armenta said.
“We're optimistic it could be less,” Armenta said.
Rivera is being housed in the juvenile justice center until he can find placement.
He wore a gray sweatshirt and khaki pants Friday and was flanked by his parents, who left the girl and another sibling with Rivera while they were at work.
The parents, Carlos Beletzuy-Lopez and Linda Walleska Beletzuy, are awaiting trial on child neglect charges.
“I don't think he fully understands what's taken place,” Armenta said of the boy, adding that he has matured since the girl's death and has goals that include attending college when he is released from custody.