That fire started around 6:30 p.m. at a home on Leonato Way near Highway 880 and Paseo Padre Parkway.
The adult and child were found on the second floor by firefighters who responded to the call. Firefighters then called police who set up barricades. Homicide detectives were called shortly thereafter.
Investigators did not go into the home until around 11 p.m. after they received a search warrant.
The identity and gender of the victims have not yet been released. One of the victims may have been a 6-year-old girl who lived inside the house.
Neighbors said the residents inside the home said they pretty much kept to themselves. One woman said they were the people that no one knew much about.
Police say there were also some other residents who live at the house, but it is unclear if they were inside when the fire broke out.
Tuesday evening occupants of the home were at the police station answering questions. A neighbor was also there answering questions.