Police described the fatal incident as “unintentional.”
Hernandez was supposed to drop the baby off at day care, police said. Instead, she went to work in Arlington, parking her car in a lot in the 200 block of North Glebe Road. Police and relatives would not give details about her occupation.
About six hours later, Hernandez left to pick up one of her other children from day care, police said.
As soon as she realized the infant was in the car, she immediately took him to the hospital, where he was pronounced dead a short time later.
In a similar case in Baltimore, 16-month-old Sabriya Towels died Friday after a relative inadvertently left her in his truck for four hours. Charges have not been filed.
According to the child-safety advocacy group Kids and Cars, charges ranging from child neglect to murder are filed in about 60 percent of such cases.
The two deaths bring the total number of children who have died this year after being forgotten in vehicles to 19, said Jan Null, a San Francisco State University researcher and meteorologist who tracks such deaths. By comparison, at least 32 children died of heat stroke in vehicles in 2012, which was the nation’s hottest year on record.
Child-safety advocates urged parents to create reminders to help them avoid the same mistake. They suggest, for example, putting a phone or purse next to the child to make it necessary to go in the back seat to retrieve them.
“Parenting is a tough job. They are juggling a lot of different priorities.” Gary Karton, spokesman for Safe Kids Worldwide, which works to stop preventable child deaths. “The mind goes on autopilot, and sometimes it results in tragedies.”
Until Friday, Hernandez supported herself and her five children, family members said.
The remaining four are now in the care of their grandparents, who live near Belle View Shopping Center.
Her family does not know the full details of what happened Friday. They said they have not been able to speak to Hernandez since her arrest.
Antonio Conde, Hernandez’s father, said that before Friday, she had been doing well, despite being on her own. He said her children are in Catholic school.
Lori Aratani and Eddy Palanzo contributed to this report.