George Allen, 37, and his five-year-old son, Geordie, are critically ill in hospital after the incident at Killowen Primary School in Lisburn on Tuesday.
Mr Allen's seven-year-old daughter, Georgia, is stable.
The vice-principal of the school resuscitated Mr Allen using a defibrillator.
Education Minister Peter Weir praised the staff's "swift response" to the "traumatic situation".
He said his "hopes and prayers" were with Mr Allen's family.
Although the school was closed on Wednesday, staff met with independent counsellors to prepare them for any questions the children might ask when they return.
Democratic Unionist Party councillor Jonathan Craig, who sits on the school's board of governors, said the vice-principal would need support after his efforts at the scene.
"I know that over the next 24 hours, the real impact of what has occurred will probably hit him.
"That's where we need specialist help to try and counsel and give guidance to him and the rest of the staff."
Mr Allen is being treated in the Ulster Hospital in Dundonald.
His children are at the Royal Belfast Hospital for Sick Children and are thought to have suffered burn injuries.

Charlene Walker, 36, suffered a single stab wound at the Darlington home of Julie Gowling in December.
The 44-year-old tried to cover up the killing and dispose of the weapon, a kitchen knife, by burying it in a garden, Teesside Crown Court heard.
Judge Mrs Justice Jefford told the mother-of-four she must serve a minimum of 14 years in prison.
The court heard Gowling, who had denied murder, got into a heated argument with Ms Walker - a known drug user - over the missing cash on 6 December.
It ended when Gowling lost her temper and stabbed Ms Walker in the chest. She then fled the house and tried to dispose of the knife.
The court was told Ms Walker died as a result of massive blood loss.
After the hearing, Det Supt Dave Ashton, of Durham Police, said: "Our condolences go to the family of Charlie Walker who, since her death have shown nothing but dignity and courage.
"Ms Walker had a difficult life in many ways but the extreme act of violence which ended her life was not justified during an argument over a relatively trivial matter."

Steve Finnigan said the county faced the harshest budget cuts in England, which could potentially see the force becoming a "blue light" service, responding to emergencies only.
Mounted and dog sections along with road policing units could be lost and community policing cut.
Since 2010, the force has axed about 700 officers and 275 members of staff.
Lancashire's Police and Crime Commissioner (PCC) said "savage" budget cuts would have a "devastating impact" on policing.
Clive Grunshaw said communities would be "left at risk" as the government continued to implement austerity cuts.
Details of the force's cuts will be revealed after the government's Comprehensive Spending Review at the end of November.
But Mr Grunshaw said proposed changes to the way forces are awarded grant funding means Lancashire will have to cut a further Â£24.8m on top of Â£74m already saved.
He said: "The likely outcome for Lancashire is far worse than we had expected.
"While the full implications are not yet clear there is no doubt that these savage cuts, which come on top of the already significant savings which have had to be made, will have a devastating impact on the standards of policing which the Constabulary is able to deliver and which our communities have come to expect."
The Home Office is yet to comment.
The education minister has commended staff at a County Antrim school for their actions after a father and his two children were hit by lightning.
[NEXT_CONCEPT]
A woman who stabbed her lodger during a row over a missing £21 has been jailed for her murder.
[NEXT_CONCEPT]
Lancashire Police will "not be viable" after 2020 because of cuts to funding, the chief constable has warned.