On Tuesday night, a woman was arrested after an incident involving two young children in the Ardoyne area in the north of the city.
After the family stabbing incident in Brompton Park, paramedics sent the two children to the hospital earlier.
The police later confirmed the death of a child.
It is understood that another child is being treated in the hospital.
“After the death of a child in the Brompton Park area north of Belfast tonight, the police have begun investigating the murder and arrested a child in this connection.” Northern Ireland Police Service spokesman.
“The investigation is still in its early stages and further information will be provided in due course.”
Parliament of North Belfast John Finucane Twitter wrote: “The police have now confirmed a murder investigation into the tragic incident in Addoin tonight, and one of them was arrested.
“We are with everyone involved.”
Nichola Mallon, deputy leader of the SDLP and North Belfast Councillor, said the local community was shocked.
“It is important to provide PSNI with sufficient space and full cooperation to fully investigate this terrible incident,” she said.
The Northern Ireland Ambulance Service received a 999 call at 8:16 on Tuesday evening.
A rapid response paramedic and two emergency personnel attended the meeting.
