The incident happened around 2:30 p.m. Monday, August 12, on Fulton Street in Bedford-Stuyvesant.
Authorities say the suspect was holding what could be a gun in his right hand as he cornered the 39-year-old victim and the kids inside the elevator.
The suspect removed the woman's jewelry and fled on a bicycle.
Police say 36-year-old Oneil Borgella was taken into custody in connection with the robbery.
He is charged with first-degree robbery, second-degree menacing and acting in a manner that could injure a child under the age of 17.
Borgella is a Level 3 sex offender, with a past conviction for raping a 14-year-old girl in 1999.
Anyone with additional information is asked to call Crime Stoppers at (800) 577-TIPS (8477).