The victims were struck while crossing at Second Avenue and East 125th Street
Both were taken to Harlem Hospital, where the seven-year-old was pronounced dead.
The woman is in stable condition.
The accident happened on the ramp that leads to the RFK Bridge.
The tow truck was heading to assist a disabled vehicle on the bridge right when the mother and young boy were crossing the street.
Sources tell Eyewitness News the driver probably never saw the two crossing the street. The tow truck is operated by the MTA Bridges & Tunnels.
The driver is being interviewed, but no criminality is suspected.
