Tucson police say the remains discovered Tuesday are believed to be those of Roman Barreras.
The boy's mother, 39-year-old Raquel Barreras, has been arrested on suspicion of first-degree murder and child abuse.
The boy's 45-year-old father, Martin Barreras, also was booked into jail Tuesday on suspicion of child abuse.
The Arizona Daily Star reports that in an interim complaint filed by police with Pima County Justice Court, the children of Raquel Barreras say she allegedly starved Roman and put his body in a toy chest in the back yard.
Police say an autopsy will determine when and how the child died.