The girl told the dispatcher her mother's foot was on the gas and she didn't know how to put the van in park.
The Volusia County Sheriff's Office said the woman, identified as 28-year-old Tiffany Smith, of Deltona, overdosed on heroin. Smith lost consciousness and her daughter called 911, authorities said.
A 911 dispatcher stayed on the phone with the girl until deputies were able to find the minivan. It was on eastbound I-4 at the 114 mile marker.
Body camera video shows the minivan on the side of the interstate. It was still on, with the lights illuminating the grass in front of it. Responding deputies divided the responsibilities of calling Animal Control to collect the dogs and taking care of the children, officials said. The baby, they observed, was still in his car seat.
Paramedics gave Smith a dose of Narcan, and deputies spoke with her when she regained consciousness, authorities said. She told them she had been taking her children to South Carolina when she started having back pain, so she took the heroin for relief, officials said.
Smith was taken to an area hospital for treatment. Deputies said she was not immediately booked into jail, pending medical treatment.
The children were not injured and were placed with their grandmother, authorities said. Volusia County Animal Control took the dogs.