The crash happened at 2:40 p.m. Tuesday on Whitesville Road (SR30), west of Whaley's Road in Delmar.
Police say 46-year-old Danielle Bobak, of Georgetown, lost control of her 2007 Subaru Legacy. The car hit a tree and rolled over.
The boy, 2-year-old Lleyton Slate, was in a car safety seat, but it was not properly installed. The child was partially ejected from the vehicle.
Slate was flown to the hospital where he was pronounced dead.
Bobak, who was wearing a seatbelt, was last reported to be in serious condition at the hospital.
Police say a preliminary investigation suggests alcohol was a factor in this crash.
Whitesville Road in the area of Whaley's Road was closed for approximately three and a half hours as the crash was investigated and cleared.
The Delaware State Police and Office of Highway Safety want to remind the public to have your car seats checked. Three out of four car seats aren't installed correctly. Free check stations are offered throughout Delaware and are listed online by visiting http://ohs.delaware.gov/carseat or by contacting the Office of Highway Safety at (302)744-2740.