The incident happened Saturday just after 3:30 a.m. as the train approached the St Lawrence Avenue Station.
A 19-year-old man was stabbed in the hip and is expected to be OK.
The NYPD says 18-year-old Parnell Shamore, a 14-year-old boy and a 16-year-old girl were charged with second-degree assault.
Shamore faces additional charges, including possession of a burglar's tool, reckless endangerment, menacing and criminal trespassing.