INDIAN RIVER COUNTY — A rollover crash on U.S. 1 killed a 4-year-old Fort Pierce girl early Thursday, according to the Florida Highway Patrol.

The young girl killed was identified by FHP as Isabella Slone. She was pronounced dead at the scene.

A 5-year-old boy and two adults sustained minor injuries, an FHP news release said.

The crash was reported about 6:15 a.m. just south of the intersection of U.S. 1 and Highland Drive.

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According to the release, Isabella and Elijah Slone, 5, were in a 2001 Saturn compact car driven south by Shaina Susan Holder, 24, of Fort Pierce.

The Saturn was traveling south in the center lane when its right front struck the left rear of a 1996 Ford F-150, said FHP Sgt. Raymond Stuhr.

The pickup, also southbound, was driven by Lloyd Norman James Mills, 61, of Vero Beach.

FHP said the reason for the collision was "undetermined." The cause of the crash is still under investigation, the release states.

St. Lucie County court records show Holder's driver's license was suspended in October after she failed to abide by conditions for probation for a driving without a valid drivers license conviction.

Holder's North Carolina drivers license was suspended when she received that citation in March, according to the St. Lucie County Sheriff's Office.

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Holder lost control of her vehicle, which rolled over several times and ejected Isabella, the release states.

"It turned sideways and started rolling down the road, flipping," said Tim Tryon, who was riding his bike nearby.

Holder wasn't wearing a seat belt, according to FHP.

Stuhr said there were two car seats in the back of the Saturn, but the children weren't properly restrained.

"That little girl flew out," Tryon said. "I didn't even want to see that."

Mills was wearing a seat belt, the FHP news release said.

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Elijah Stone, Holder and Mills were taken by ambulance to Indian River Medical Center, Ruiz said. They were all released Thursday afternoon, hospital officials said. 

All southbound lanes on U.S. 1 were closed for about six hours after the crash.

Investigators spent hours interviewing witnesses and taking photos and measurements at the scene.

The road reopened about 12:15 p.m.