Manhattan Assistant District Attorney Nicole Blumberg told a judge Wednesday she plans to seek the new charge against Kryzie King.
Defense lawyer Bryan Konoski declined to comment.
The boy, Myls Dobson, died Jan. 8. He was in King's care while his father was jailed.
Medical examiners ruled his death a homicide this month. They determined he died of child abuse, including dehydration.
Before the finding, King was charged with assault and pleaded not guilty.
According to prosecutors' court documents, King told police she beat the boy with a belt and wires, bound him with shoelaces and locked him on a freezing terrace because he misbehaved.