Authorities say the driver, 50-year-old Felix Del Valle, and 58-year-old matron Lucilla Cruz were both taken into custody.
They are charged with failure to exercise control of a minor.
According to police, Del Valle parked his bus at the depot on Chelsea Road at around 1:30 p.m. Wednesday without spotting the girl still on board.
She was on the bus for about four hours before another employee noticed her.
The girl, who was supposed to be dropped off at Little Lamb Pre School, was taken to the hospital to be checked out.
She was returned to the parents at around 6 p.m.
The driver and matron are employed by Consolidated Bus Transit.
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