Christopher Valdez's 28-year-old mother and her boyfriend were charged on Sunday in connection with his death. Valdez died on Friday on his fourth birthday.
CBS Chicago reported that police said Cesar Ruiz, 34, was charged on Friday with first-degree murder and for concealing a homicide in Christopher Valdez's death.
The 4-year-old's mother, Crystal Valdez, was also charged with endangering the life of a child and concealing a homicide, according to news reports.
Police has told the media that there was a possible domestic situation at the boy's home. Authorities are yet to say what caused the boy's death.
Cook County medical examiner's office told CBS that an autopsy on Saturday reportedly determined the boy died from multiple blunt force injuries and child abuse.
Fox News reported that the boy's grandfather, Tom Valdez, said relatives who arrived at the house that day to deliver a birthday cake, found the Christopher Valdez's body and alerted police.
The boy was dead when police arrived.