The family are believed to be from the Churchtown area, just a few miles from where the van being driven by the man crashed with a tractor on a regional road near Buttevant shortly before 1pm yesterday.
It is understood the man’s partner and her children were in a car just behind the van and happened on the scene moments later.
They are believed to have been heading for a family trip to the beach on one of the hottest days of the year, when the crash happened on the road between Buttevant and Liscarroll.
The driver of the van was pronounced dead at the scene, soon after emergency services arrived.
The 15-year-old girl was airlifted to hospital and the other passenger in the van, a 17-year-old boy, was also taken by helicopter to Cork University Hospital.
Both are believed to have been in a serious condition last night, and were removed from the scene only after extremely careful work by emergency services to free them from the badly damaged van.
The driver of the tractor, a man in his 20s, was unharmed in the accident, according to gardaí.
Gardaí are appealing for anyone with information or who witnessed the crash to contact them at Mallow Garda station on 022 31450.
The crash happened about three miles from Buttevant on the R522, as temperatures pushed towards the mid-20s.
The site was examined by Garda forensic collision investigators and a Garda public service vehicle officer.
An autopsy on the man’s body will take place at Cork University Hospital.