Police and paramedics were called to a residence on the 800 block of West J Street in Ontario by a report of a child not breathing at about 9:19 a.m. Tuesday.
CPR was performed on the 7-month-old baby boy, who was then hospitalized with life-threatening injuries. Medical personnel noted injuries consistent with possible child abuse, Ontario Police said Wednesday.
Ontario resident Ryan Anthony Garcia, 21, and his girlfriend were babysitting for the child's mother, police said. The girlfriend called 911 when the baby stopped breathing.
Detectives determined Garcia became upset with the child and inflicted severe injuries on the baby, causing the child to stop breathing.
Garcia was arrested for attempted murder and booked at West Valley Detention Center in Rancho Cucamonga.
Anyone with information related to the case is asked to contact Detective Jeff Wentz at (909) 395-2715.