Police say the bus struck a guardrail and landed on its side on Express Drive South, just west of Wicks Road around 10:30 a.m.
Four children were on the bus and were taken to local hospitals for evaluation.
The children attend Building Blocks Preschool in Commack and all parents were notified.
The driver, a man, and aide, a woman, were transported to local hospitals for treatment of minor injuries.
The Long Island Expressway Service Road was closed between Exit 52 and Wicks Road during the investigation.
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