My bet is the majority died of disease.
This place was a hell hole where kids were dumped into,
By modern standards, all southern detention facilities prior to the latter half of the 20th century were hellholes.
even orphans who were abandoned by their parents
Dozier was not an orphanage.
or those who were incarcerated for rather minor crimes
I suspect you will find long rap sheets and a judges warning about "the next time" prior to the "minor" crime.
who were subjected to sadistic beatings,
Unfortunately, this was widespread, even in mental hospitals.
many of which resulted in deaths that the school never recorded, their family members never informed of their deaths or allowed to give them proper burials.
In the first half of the 20th century in Florida, notification of next of kin, especially when next of kin may have been unknown would have been difficult.
People back then buried the dead near where they died, placed a makeshift wooden cross on the grave and moved on. Within a year, or two, the wooden marker would have rotted away.
Sounds like Haut de la Garenne children’s home.