At about 1 p.m. Friday, police responded to the 1300 block of Leonard Drive after being contacted by a woman who was a care provider for the little girl. The girl suffered from physical and mental disabilities, police said.
The woman told officers that she found the mother and child inside a car in the home's garage with a running motor and a hose leading from the tail pipe to the interior, according to police.
The mother was conscious when the care provider found her, but the girl was not, police said.
Alameda County fire officials transported mother and child to local hospitals. Subsequently, the girl was pronounced dead by medical staff.
The mother, 53-year-old Christel Johnson, is expected to survive, police said.
This case is being actively investigated as the third homicide in San Leandro this year, according to police.