The boy's burns, mostly below the waist, were getting worse and a doctor was having trouble treating him because he didn't know what kind of chemical agent was used.
The pickup truck was found Monday along the side of Interstate 95 near West Palm Beach. The children's father, Jorge Barahona, was lying on the ground near the truck with severe burns, apparently from gasoline he poured on himself because he wanted to commit suicide after he put his dead daughter in a bag and loaded her into the truck, according to police documents. The boy was in the front seat of the vehicle, having seizures.
Dr. Walter Lambert said the hospital was considering moving the boy, who has woken up a few times but hasn't spoken, to a burn unit.
Because of the toxic fumes, the girl's body wasn't located until hours later, officials said.
Barahona has been charged with aggravated child abuse, but authorities expect more charges, West Palm Beach city spokesman Chase Scott said. Barahona, 53, is currently in intensive care at a hospital.
The father told officers he gave his son a handful of sleeping pills and, with the boy's head in his lap, poured gasoline on himself, the report said. It's not clear when the father allegedley doused the boy, Victor, with acid.
He told police he intended to light himself on fire he said he could not do it because the boy was in the truck with him, the report said. When police asked why he didn't have similar burns to his son, he said some of the gasoline must have splattered on his son.
"Jorge's account of events is inconsistent," the report said.
Fumes from the boy were so toxic, workers were overcome just by being close to him when they were wheeling him into the hospital. Four firefighters working the scene were also treated for chemical exposure.
Doctors also found that the boy had previously broken his collarbone and an arm, and he had marks on his wrists and other scars on his body, the documents said.
Barahona's first court appearance was scheduled Thursday.
Barahona and his wife, Carmen, adopted four children with special needs from foster care. At a custody hearing Wednesday for the other two children, a judge blasted a state child welfare worker for not throughly following up on an anonymous allegation that came into their hotline Feb. 10, saying the twins' feet and hands were bound with duct tape and they were kept in a bathtub as punishment.
An investigator, Angela Fleary, went to the home but couldn't find the father or the twins. Carmen had told them she was separated from her husband and didn't know where he or the twins were, but officials now believe she was covering for him. The investigator also did not interview the two other children in the home, ages 11 and 7. The anonymous tip, it turns out, came from the 7-year-old, who told a relative who called the hotline.
"How could we have gotten a call to a hotline on Feb. 10 and a child died" a few days later, Judge Cindy Lederman said at the hearing.
When asked why the investigator didn't interview the kids, she said it was 9 p.m. on a Friday night. The judge was furious with the answer.
Carmen Barahona was at the court hearing, but stood with a piece of paper covering her face. At times, she cried. Her attorney, Grissel Picot, said she didn't want to comment.
The Department of Children and Families investigated three allegations of child abuse or neglect in the past several years, but a spokesman said they were closed with some or no indicators of abuse or neglect.
A police cruiser was parked outside the couple's modest orange one story house and the front of house was cordoned off with crime scene tape. The yard has tropical landscape, including palm trees and a wrought-iron fence.
Neighbors said they didn't even realize that children stayed at the home.
"I never saw these kids outside. No one knows anything about this family," said neighbor Gerardo Rodriguez, 72.
DCF has placed the Barahona's two other children with in a foster home.
Records showed Barahona and his wife ran CJ's Pest Exterminator Inc. out of their home, but the business was listed as "inactive" for not registering in 2010.
Associated Press writer Jennifer Kay contributed to this report in Miami and Matt Sedensky in West Palm Beach.