The boy was brought to the Ceressas Enrichment and Empowerment Academy on Monday, Broward County Sheriff's spokeswoman Keyla Concepcion said, "What happened between then and the time he was found dead in the van has been?
Oakland Park's sheriff's office and firefighters were called at around 15:20, CNN member WSVN said. At temperatures in the low nineties, according to the authorities, the heat could have been the cause of death according to the partner.
The sheriff's office is interviewing staff members and investigating the incident, Concepcion said, adding that it was too early to say whether an indictment was being filed.
If heat is confirmed as the cause of death, it is the 24th time a child died in a hot car in the US this year, according to NoHeatStroke.org and the security organization Kids and Cars.
One-year-old twin babies died in New York on Friday after being left in an eight-hour car. The father of the children was charged with two manslaughter and two negligent crimes.