Authorities say the infant was not breathing when he was taken by ambulance to Centinela Hospital Sunday. He was pronounced dead at the hospital at 11:45 p.m.
After preliminary investigation, detectives arrested the mother, 42-year-old Sandra Cartegna, for child endangerment, and her boyfriend, 44-year-old Julio Mejia, for murder. Both suspects are being held at the Hawthorne Police Department on $100,000 bail.
The cause of the infant's death has not been released. An autopsy is scheduled for later this week.
"Obviously, a 14-month-old infant doesn't usually get into that sort of trouble. And if it is, it's very obvious if something falls on them or something like that, or you know, suffocate for some reason. But evidently, the injuries to this child were such that it was obvious that the doctor called homicide," said Sgt. Rich Pena with the Los Angeles County Sheriff's Department.
Cartegna's 9-year-old and 14-year-old sons were taken into protective custody as the investigation continues.
Anyone with information is urged to call Crime Stoppers at (800) 222-TIPS.