Police say a white box truck struck the two male victims as they rode a single bicycle.
The truck kept going southbound on Hicksville Road, investigators said.
Both victims were taken to the hospital where one was pronounced dead.
The other victim remained in critical condition with internal injuries.
Names of the victims have not been released.
Anyone who may have seen this accident is asked to call Nassau County Crime Stoppers at 1-800-244-TIPS. All callers will remain anonymous.