The deaths of two Bronx toddlers were ruled homicides on Tuesday, the city medical examiner's office said, citing blunt impact injuries to the children's bodies.

The ruling was announced not long after police released the mother's boyfriend, 31-year-old Jordan Novell, after lengthy questioning, police sources said. 

The two children — 2-year-old Olivia Gee and her 3-year-old brother, Micha Gee — were rushed to the hospital with breathing problems early Monday after they were discovered unconscious and unresponsive by Novell just before 1:20 a.m., police sources said.

Both children appeared to have slight bruising on their necks, and Olivia showed signs of blunt force trauma to her abdomen, a source said before the medical examiner's ruling.

Both Novell and the children’s mother, Jade Spencer, 31, were considered persons of interest in the case. Novell was still cooperating with investigators late Tuesday afternoon, police said.

Spencer, meanwhile, has been hospitalized for a psychiatric evaluation, police said.

Mayor Bill de Blasio released a statement Tuesday saying the Administration for Children's Services is part of the investigation. 

"Our city is mourning the loss of two young children in a tragedy Monday in the Bronx. As a parent, it’s very painful for me to think about the death of these two children and what the family is going through right now," the statement said. "The NYC Police Department and Administration for Children’s Services will continue to investigate this tragedy."

The children had gone to bed hours before they died, at about 8:30 p.m. on Sunday, according to police. They were rushed from their apartment on Van Cortlandt Park South to Montefiore Medical Center, where they were pronounced dead.