Boy, 3, found dead in NYC apartment, after mom leaves him with babysitter upstairs

A 3-year-old boy was found dead with head injuries Sunday night – after his mom left him with a neighbor upstairs from their own Brooklyn apartment, cops and sources said.

The toddler was discovered unconscious and unresponsive inside an apartment on New York Avenue near Snyder Avenue in East Flatbush around 9:45 p.m. — and it wasn’t the apartment where he’d been dropped off, according to the NYPD and sources.

The boy, who suffered injuries to the head, was taken to the Kings County Hospital Center, where he was pronounced dead.

The tot’s mother had previously left her young son with a 54-year-old man who lived upstairs, police sources said.

But the tot was not found in the apartment where his mom left him — and instead discovered mortally injured inside a neighboring unit, the sources said.

The neighbor’s stepson, 29, was taken into custody for questioning, according to the sources.

The younger man was also wanted on a warrant in connection to a previous petit larceny, the sources said.

The NYPD confirmed that the boy’s death is being eyed as suspicious because of his head injuries, but said that the official cause of death will be determined by the city medical examiner’s office.