Sources tell NY1 police want to question the mother of the two Bronx toddlers beaten to death earlier this week.
The mother's boyfriend is also being questioned by investigators.
The city Medical Examiner's Office ruled the deaths of two-year-old Olivia Gee and her three year-old brother Micha homicides.
They suffered blunt impact injuries to the torso.
Sources tell NY1 the children also had a history of respiratory issues.
The NYPD says it got a 911 call early Monday morning that they were having trouble breathing inside their Kingsbridge home.
The toddlers were rushed to the hospital, where they were pronounced dead.
Sources say both the mother and boyfriend are persons of interest in the case. Sources also say the mother has a history of mental health issues.
"The worst things that usually happen around here are car break-ins, so this kind of news is going to rock this neighborhood," said one person in the neighborhood.
"All too often we are seeing in the news today these types of stories," said another. "Your mind can’t conceptualize the deaths of children. It’s not supposed to be this way. It’s not the natural order of things."
The Administration for Children's Services is investigating.