Investigators allege Vences-Garcia recruited four people, including two teens, to carry out the abduction of Adrian Jaimes.
Vences-Garcia's cousin, Salvadore Hernandez, is the child's father.
The kidnappers opened the door of the family's car Thursday as the children's mother was about to take them to school, police said.
The boy was found safe Thursday night in a North Austin neighborhood. Police said they believe public attention about the abduction pressured the abductors to drop off the child unharmed in a populated area.
Adrian's 10-year-old sister was the initial target, police said. But the girl had recently reported that someone in a suspicious car had followed her to school, the Austin American-Statesman reported in its online edition Monday.
"We know this was motivated by money," Austin police Cmdr. Julie O'Brien said. "He wanted a lot of money."
O'Brien said Vences-Garcia told some associates he wanted $150,000 from the family. Police said a family member got two anonymous cell phone calls demanding $300,000 for the child's safe return.
Police said it wasn't clear why Vences-Garcia thought he was owed money.
Vences-Garcia was initially arrested on outstanding drug possession and drunken driving warrants. He also is accused of immigration violations.
Authorities also have charged Esau Alejandro Rodriguez-Flores, 17, and Hector Luis Hernandez, 19, with aggravated kidnapping. Two unidentified juveniles also have been charged.
Hernandez was being held on $500,000 bond Monday night in the Travis County Jail. It wasn't immediately clear if he had an attorney.
Meanwhile, officials said a 911 operator who had been criticized by police as "unduly harsh" with Adrian's mother when she reported the abduction has chosen to retire. The operator, Victor Cervantes, has worked in the dispatch center for 22 years. Officials say he made Zuleima Jaimes wait more than four minutes before telling her police were on the way and told her to stop crying so he could hear her better.
