Kiara Morant, 18, was driving an SUV around 4:30 p.m. when she crashed into a fenced playground area where the two girls were playing at the Imagination Station Learning Center Preschool in Arcadia, about 90 miles southeast of Tampa.
"All she was doing was playing in the playground. We just want her back. We want her back," Josephine Valdez, the grandmother of the girl who was killed, told FOX 13 Tampa.
According to a crash report, Morant -- who did not have a valid driver's license -- was traveling on East Magnolia Street in a Jeep Cherokee when she drove over a raised concrete curb, hit a street sign, crossed the sidewalk, and crashed into a chain-link fence at the corner of the preschool.
Troopers said the Jeep then drove into the playground, where it struck several other wooden-support posts and playground equipment. The two girls who were playing in that area were struck by the vehicle, which eventually stopped after crashing into a tree.
The 4-year-old girl was taken to Gulf Coast Hospital where she died, while the 5-year-old girl was taken to DeSoto Memorial Hospital in serious condition.
"We said our last goodbye to her last night, holding her hand. Just begging, please come back. Please don’t go," Valdez said, according to FOX 13.
Morant, who had minor injuries following the crash, was arrested for not having a valid driver's license. Morant bonded out of jail before the child died, troopers said, noting she could face additional charges.
"Right now this driver faces several felony charges, just based simply upon the fact that she was not properly licensed," Trooper Ken Watson told FOX 13. "Flat out should not have been behind the wheel at the time."
A memorial with balloons and toys was set up outside the playground following the deadly crash.
The incident remains under investigation, authorities said.